Merge tag 'erofs-for-6.11-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs

Pull erofs updates from Gao Xiang:
 "Updates for folio conversions for compressed inodes: While large folio
  support for compressed data could work now, it remains disabled since
  the stress test could hang due to page migration in a few hours after
  enabling it. I need more time to investigate further before enabling
  this feature.

  Additionally, clean up stream decompressors and tracepoints for
  simplicity.

  Summary:

   - More folio conversions for compressed inodes

   - Stream decompressor (LZMA/DEFLATE/ZSTD) cleanups

   - Minor tracepoint cleanup"

* tag 'erofs-for-6.11-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs:
  erofs: silence uninitialized variable warning in z_erofs_scan_folio()
  erofs: avoid refcounting short-lived pages
  erofs: get rid of z_erofs_map_blocks_iter_* tracepoints
  erofs: tidy up stream decompressors
  erofs: refine z_erofs_{init,exit}_subsystem()
  erofs: move each decompressor to its own source file
  erofs: tidy up `struct z_erofs_bvec`
  erofs: teach z_erofs_scan_folios() to handle multi-page folios
  erofs: convert z_erofs_read_fragment() to folios
  erofs: convert z_erofs_pcluster_readmore() to folios

10 files changed, 496 insertions, 646 deletions

diff --git a/fs/erofs/compress.h b/fs/erofs/compress.h
index 19d53c30c8af..7bfe251680ec 100644
--- a/fs/erofs/compress.h
+++ b/fs/erofs/compress.h
@@ -24,6 +24,8 @@ struct z_erofs_decompressor {
 		      void *data, int size);
 	int (*decompress)(struct z_erofs_decompress_req *rq,
 			  struct page **pagepool);
+	int (*init)(void);
+	void (*exit)(void);
 	char *name;
 };
 
@@ -52,17 +54,14 @@ struct z_erofs_decompressor {
  */
 
 /*
- * short-lived pages are pages directly from buddy system with specific
- * page->private (no need to set PagePrivate since these are non-LRU /
- * non-movable pages and bypass reclaim / migration code).
+ * Currently, short-lived pages are pages directly from buddy system
+ * with specific page->private (Z_EROFS_SHORTLIVED_PAGE).
+ * In the future world of Memdescs, it should be type 0 (Misc) memory
+ * which type can be checked with a new helper.
  */
 static inline bool z_erofs_is_shortlived_page(struct page *page)
 {
-	if (page->private != Z_EROFS_SHORTLIVED_PAGE)
-		return false;
-
-	DBG_BUGON(page->mapping);
-	return true;
+	return page->private == Z_EROFS_SHORTLIVED_PAGE;
 }
 
 static inline bool z_erofs_put_shortlivedpage(struct page **pagepool,
@@ -70,32 +69,32 @@ static inline bool z_erofs_put_shortlivedpage(struct page **pagepool,
 {
 	if (!z_erofs_is_shortlived_page(page))
 		return false;
-
-	/* short-lived pages should not be used by others at the same time */
-	if (page_ref_count(page) > 1) {
-		put_page(page);
-	} else {
-		/* follow the pcluster rule above. */
-		erofs_pagepool_add(pagepool, page);
-	}
+	erofs_pagepool_add(pagepool, page);
 	return true;
 }
 
+extern const struct z_erofs_decompressor z_erofs_lzma_decomp;
+extern const struct z_erofs_decompressor z_erofs_deflate_decomp;
+extern const struct z_erofs_decompressor z_erofs_zstd_decomp;
+extern const struct z_erofs_decompressor *z_erofs_decomp[];
+
+struct z_erofs_stream_dctx {
+	struct z_erofs_decompress_req *rq;
+	unsigned int inpages, outpages;	/* # of {en,de}coded pages */
+	int no, ni;			/* the current {en,de}coded page # */
+
+	unsigned int avail_out;		/* remaining bytes in the decoded buffer */
+	unsigned int inbuf_pos, inbuf_sz;
+					/* current status of the encoded buffer */
+	u8 *kin, *kout;			/* buffer mapped pointers */
+	void *bounce;			/* bounce buffer for inplace I/Os */
+	bool bounced;			/* is the bounce buffer used now? */
+};
+
+int z_erofs_stream_switch_bufs(struct z_erofs_stream_dctx *dctx, void **dst,
+			       void **src, struct page **pgpl);
 int z_erofs_fixup_insize(struct z_erofs_decompress_req *rq, const char *padbuf,
 			 unsigned int padbufsize);
-extern const struct z_erofs_decompressor erofs_decompressors[];
-
-/* prototypes for specific algorithms */
-int z_erofs_load_lzma_config(struct super_block *sb,
-			struct erofs_super_block *dsb, void *data, int size);
-int z_erofs_load_deflate_config(struct super_block *sb,
-			struct erofs_super_block *dsb, void *data, int size);
-int z_erofs_load_zstd_config(struct super_block *sb,
-			struct erofs_super_block *dsb, void *data, int size);
-int z_erofs_lzma_decompress(struct z_erofs_decompress_req *rq,
-			    struct page **pagepool);
-int z_erofs_deflate_decompress(struct z_erofs_decompress_req *rq,
-			       struct page **pagepool);
-int z_erofs_zstd_decompress(struct z_erofs_decompress_req *rq,
-			    struct page **pgpl);
+int __init z_erofs_init_decompressor(void);
+void z_erofs_exit_decompressor(void);
 #endif
diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
index 9d85b6c11c6b..c2253b6a5416 100644
--- a/fs/erofs/decompressor.c
+++ b/fs/erofs/decompressor.c
@@ -2,6 +2,7 @@
 /*
  * Copyright (C) 2019 HUAWEI, Inc.
  *             https://www.huawei.com/
+ * Copyright (C) 2024 Alibaba Cloud
  */
 #include "compress.h"
 #include <linux/lz4.h>
@@ -109,7 +110,6 @@ static int z_erofs_lz4_prepare_dstpages(struct z_erofs_lz4_decompress_ctx *ctx,
 
 		if (top) {
 			victim = availables[--top];
-			get_page(victim);
 		} else {
 			victim = __erofs_allocpage(pagepool, rq->gfp, true);
 			if (!victim)
@@ -371,40 +371,113 @@ static int z_erofs_transform_plain(struct z_erofs_decompress_req *rq,
 	return 0;
 }
 
-const struct z_erofs_decompressor erofs_decompressors[] = {
-	[Z_EROFS_COMPRESSION_SHIFTED] = {
+int z_erofs_stream_switch_bufs(struct z_erofs_stream_dctx *dctx, void **dst,
+			       void **src, struct page **pgpl)
+{
+	struct z_erofs_decompress_req *rq = dctx->rq;
+	struct super_block *sb = rq->sb;
+	struct page **pgo, *tmppage;
+	unsigned int j;
+
+	if (!dctx->avail_out) {
+		if (++dctx->no >= dctx->outpages || !rq->outputsize) {
+			erofs_err(sb, "insufficient space for decompressed data");
+			return -EFSCORRUPTED;
+		}
+
+		if (dctx->kout)
+			kunmap_local(dctx->kout);
+		dctx->avail_out = min(rq->outputsize, PAGE_SIZE - rq->pageofs_out);
+		rq->outputsize -= dctx->avail_out;
+		pgo = &rq->out[dctx->no];
+		if (!*pgo && rq->fillgaps) {		/* deduped */
+			*pgo = erofs_allocpage(pgpl, rq->gfp);
+			if (!*pgo) {
+				dctx->kout = NULL;
+				return -ENOMEM;
+			}
+			set_page_private(*pgo, Z_EROFS_SHORTLIVED_PAGE);
+		}
+		if (*pgo) {
+			dctx->kout = kmap_local_page(*pgo);
+			*dst = dctx->kout + rq->pageofs_out;
+		} else {
+			*dst = dctx->kout = NULL;
+		}
+		rq->pageofs_out = 0;
+	}
+
+	if (dctx->inbuf_pos == dctx->inbuf_sz && rq->inputsize) {
+		if (++dctx->ni >= dctx->inpages) {
+			erofs_err(sb, "invalid compressed data");
+			return -EFSCORRUPTED;
+		}
+		if (dctx->kout) /* unlike kmap(), take care of the orders */
+			kunmap_local(dctx->kout);
+		kunmap_local(dctx->kin);
+
+		dctx->inbuf_sz = min_t(u32, rq->inputsize, PAGE_SIZE);
+		rq->inputsize -= dctx->inbuf_sz;
+		dctx->kin = kmap_local_page(rq->in[dctx->ni]);
+		*src = dctx->kin;
+		dctx->bounced = false;
+		if (dctx->kout) {
+			j = (u8 *)*dst - dctx->kout;
+			dctx->kout = kmap_local_page(rq->out[dctx->no]);
+			*dst = dctx->kout + j;
+		}
+		dctx->inbuf_pos = 0;
+	}
+
+	/*
+	 * Handle overlapping: Use the given bounce buffer if the input data is
+	 * under processing; Or utilize short-lived pages from the on-stack page
+	 * pool, where pages are shared among the same request.  Note that only
+	 * a few inplace I/O pages need to be doubled.
+	 */
+	if (!dctx->bounced && rq->out[dctx->no] == rq->in[dctx->ni]) {
+		memcpy(dctx->bounce, *src, dctx->inbuf_sz);
+		*src = dctx->bounce;
+		dctx->bounced = true;
+	}
+
+	for (j = dctx->ni + 1; j < dctx->inpages; ++j) {
+		if (rq->out[dctx->no] != rq->in[j])
+			continue;
+		tmppage = erofs_allocpage(pgpl, rq->gfp);
+		if (!tmppage)
+			return -ENOMEM;
+		set_page_private(tmppage, Z_EROFS_SHORTLIVED_PAGE);
+		copy_highpage(tmppage, rq->in[j]);
+		rq->in[j] = tmppage;
+	}
+	return 0;
+}
+
+const struct z_erofs_decompressor *z_erofs_decomp[] = {
+	[Z_EROFS_COMPRESSION_SHIFTED] = &(const struct z_erofs_decompressor) {
 		.decompress = z_erofs_transform_plain,
 		.name = "shifted"
 	},
-	[Z_EROFS_COMPRESSION_INTERLACED] = {
+	[Z_EROFS_COMPRESSION_INTERLACED] = &(const struct z_erofs_decompressor) {
 		.decompress = z_erofs_transform_plain,
 		.name = "interlaced"
 	},
-	[Z_EROFS_COMPRESSION_LZ4] = {
+	[Z_EROFS_COMPRESSION_LZ4] = &(const struct z_erofs_decompressor) {
 		.config = z_erofs_load_lz4_config,
 		.decompress = z_erofs_lz4_decompress,
+		.init = z_erofs_gbuf_init,
+		.exit = z_erofs_gbuf_exit,
 		.name = "lz4"
 	},
 #ifdef CONFIG_EROFS_FS_ZIP_LZMA
-	[Z_EROFS_COMPRESSION_LZMA] = {
-		.config = z_erofs_load_lzma_config,
-		.decompress = z_erofs_lzma_decompress,
-		.name = "lzma"
-	},
+	[Z_EROFS_COMPRESSION_LZMA] = &z_erofs_lzma_decomp,
 #endif
 #ifdef CONFIG_EROFS_FS_ZIP_DEFLATE
-	[Z_EROFS_COMPRESSION_DEFLATE] = {
-		.config = z_erofs_load_deflate_config,
-		.decompress = z_erofs_deflate_decompress,
-		.name = "deflate"
-	},
+	[Z_EROFS_COMPRESSION_DEFLATE] = &z_erofs_deflate_decomp,
 #endif
 #ifdef CONFIG_EROFS_FS_ZIP_ZSTD
-	[Z_EROFS_COMPRESSION_ZSTD] = {
-		.config = z_erofs_load_zstd_config,
-		.decompress = z_erofs_zstd_decompress,
-		.name = "zstd"
-	},
+	[Z_EROFS_COMPRESSION_ZSTD] = &z_erofs_zstd_decomp,
 #endif
 };
 
@@ -432,6 +505,7 @@ int z_erofs_parse_cfgs(struct super_block *sb, struct erofs_super_block *dsb)
 	offset = EROFS_SUPER_OFFSET + sbi->sb_size;
 	alg = 0;
 	for (algs = sbi->available_compr_algs; algs; algs >>= 1, ++alg) {
+		const struct z_erofs_decompressor *dec = z_erofs_decomp[alg];
 		void *data;
 
 		if (!(algs & 1))
@@ -443,16 +517,13 @@ int z_erofs_parse_cfgs(struct super_block *sb, struct erofs_super_block *dsb)
 			break;
 		}
 
-		if (alg >= ARRAY_SIZE(erofs_decompressors) ||
-		    !erofs_decompressors[alg].config) {
+		if (alg < Z_EROFS_COMPRESSION_MAX && dec && dec->config) {
+			ret = dec->config(sb, dsb, data, size);
+		} else {
 			erofs_err(sb, "algorithm %d isn't enabled on this kernel",
 				  alg);
 			ret = -EOPNOTSUPP;
-		} else {
-			ret = erofs_decompressors[alg].config(sb,
-					dsb, data, size);
 		}
-
 		kfree(data);
 		if (ret)
 			break;
@@ -460,3 +531,28 @@ int z_erofs_parse_cfgs(struct super_block *sb, struct erofs_super_block *dsb)
 	erofs_put_metabuf(&buf);
 	return ret;
 }
+
+int __init z_erofs_init_decompressor(void)
+{
+	int i, err;
+
+	for (i = 0; i < Z_EROFS_COMPRESSION_MAX; ++i) {
+		err = z_erofs_decomp[i] ? z_erofs_decomp[i]->init() : 0;
+		if (err) {
+			while (--i)
+				if (z_erofs_decomp[i])
+					z_erofs_decomp[i]->exit();
+			return err;
+		}
+	}
+	return 0;
+}
+
+void z_erofs_exit_decompressor(void)
+{
+	int i;
+
+	for (i = 0; i < Z_EROFS_COMPRESSION_MAX; ++i)
+		if (z_erofs_decomp[i])
+			z_erofs_decomp[i]->exit();
+}
diff --git a/fs/erofs/decompressor_deflate.c b/fs/erofs/decompressor_deflate.c
index 3a3461561a3c..5070d2fcc737 100644
--- a/fs/erofs/decompressor_deflate.c
+++ b/fs/erofs/decompressor_deflate.c
@@ -15,7 +15,7 @@ static DECLARE_WAIT_QUEUE_HEAD(z_erofs_deflate_wq);
 
 module_param_named(deflate_streams, z_erofs_deflate_nstrms, uint, 0444);
 
-void z_erofs_deflate_exit(void)
+static void z_erofs_deflate_exit(void)
 {
 	/* there should be no running fs instance */
 	while (z_erofs_deflate_avail_strms) {
@@ -41,7 +41,7 @@ void z_erofs_deflate_exit(void)
 	}
 }
 
-int __init z_erofs_deflate_init(void)
+static int __init z_erofs_deflate_init(void)
 {
 	/* by default, use # of possible CPUs instead */
 	if (!z_erofs_deflate_nstrms)
@@ -49,7 +49,7 @@ int __init z_erofs_deflate_init(void)
 	return 0;
 }
 
-int z_erofs_load_deflate_config(struct super_block *sb,
+static int z_erofs_load_deflate_config(struct super_block *sb,
 			struct erofs_super_block *dsb, void *data, int size)
 {
 	struct z_erofs_deflate_cfgs *dfl = data;
@@ -97,27 +97,26 @@ failed:
 	return -ENOMEM;
 }
 
-int z_erofs_deflate_decompress(struct z_erofs_decompress_req *rq,
-			       struct page **pgpl)
+static int z_erofs_deflate_decompress(struct z_erofs_decompress_req *rq,
+				      struct page **pgpl)
 {
-	const unsigned int nrpages_out =
-		PAGE_ALIGN(rq->pageofs_out + rq->outputsize) >> PAGE_SHIFT;
-	const unsigned int nrpages_in =
-		PAGE_ALIGN(rq->inputsize) >> PAGE_SHIFT;
 	struct super_block *sb = rq->sb;
-	unsigned int insz, outsz, pofs;
+	struct z_erofs_stream_dctx dctx = {
+		.rq = rq,
+		.inpages = PAGE_ALIGN(rq->inputsize) >> PAGE_SHIFT,
+		.outpages = PAGE_ALIGN(rq->pageofs_out + rq->outputsize)
+				>> PAGE_SHIFT,
+		.no = -1, .ni = 0,
+	};
 	struct z_erofs_deflate *strm;
-	u8 *kin, *kout = NULL;
-	bool bounced = false;
-	int no = -1, ni = 0, j = 0, zerr, err;
+	int zerr, err;
 
 	/* 1. get the exact DEFLATE compressed size */
-	kin = kmap_local_page(*rq->in);
-	err = z_erofs_fixup_insize(rq, kin + rq->pageofs_in,
-			min_t(unsigned int, rq->inputsize,
-			      sb->s_blocksize - rq->pageofs_in));
+	dctx.kin = kmap_local_page(*rq->in);
+	err = z_erofs_fixup_insize(rq, dctx.kin + rq->pageofs_in,
+			min(rq->inputsize, sb->s_blocksize - rq->pageofs_in));
 	if (err) {
-		kunmap_local(kin);
+		kunmap_local(dctx.kin);
 		return err;
 	}
 
@@ -134,102 +133,35 @@ again:
 	spin_unlock(&z_erofs_deflate_lock);
 
 	/* 3. multi-call decompress */
-	insz = rq->inputsize;
-	outsz = rq->outputsize;
 	zerr = zlib_inflateInit2(&strm->z, -MAX_WBITS);
 	if (zerr != Z_OK) {
 		err = -EIO;
 		goto failed_zinit;
 	}
 
-	pofs = rq->pageofs_out;
-	strm->z.avail_in = min_t(u32, insz, PAGE_SIZE - rq->pageofs_in);
-	insz -= strm->z.avail_in;
-	strm->z.next_in = kin + rq->pageofs_in;
+	rq->fillgaps = true;	/* DEFLATE doesn't support NULL output buffer */
+	strm->z.avail_in = min(rq->inputsize, PAGE_SIZE - rq->pageofs_in);
+	rq->inputsize -= strm->z.avail_in;
+	strm->z.next_in = dctx.kin + rq->pageofs_in;
 	strm->z.avail_out = 0;
+	dctx.bounce = strm->bounce;
 
 	while (1) {
-		if (!strm->z.avail_out) {
-			if (++no >= nrpages_out || !outsz) {
-				erofs_err(sb, "insufficient space for decompressed data");
-				err = -EFSCORRUPTED;
-				break;
-			}
-
-			if (kout)
-				kunmap_local(kout);
-			strm->z.avail_out = min_t(u32, outsz, PAGE_SIZE - pofs);
-			outsz -= strm->z.avail_out;
-			if (!rq->out[no]) {
-				rq->out[no] = erofs_allocpage(pgpl, rq->gfp);
-				if (!rq->out[no]) {
-					kout = NULL;
-					err = -ENOMEM;
-					break;
-				}
-				set_page_private(rq->out[no],
-						 Z_EROFS_SHORTLIVED_PAGE);
-			}
-			kout = kmap_local_page(rq->out[no]);
-			strm->z.next_out = kout + pofs;
-			pofs = 0;
-		}
-
-		if (!strm->z.avail_in && insz) {
-			if (++ni >= nrpages_in) {
-				erofs_err(sb, "invalid compressed data");
-				err = -EFSCORRUPTED;
-				break;
-			}
-
-			if (kout) { /* unlike kmap(), take care of the orders */
-				j = strm->z.next_out - kout;
-				kunmap_local(kout);
-			}
-			kunmap_local(kin);
-			strm->z.avail_in = min_t(u32, insz, PAGE_SIZE);
-			insz -= strm->z.avail_in;
-			kin = kmap_local_page(rq->in[ni]);
-			strm->z.next_in = kin;
-			bounced = false;
-			if (kout) {
-				kout = kmap_local_page(rq->out[no]);
-				strm->z.next_out = kout + j;
-			}
-		}
-
-		/*
-		 * Handle overlapping: Use bounced buffer if the compressed
-		 * data is under processing; Or use short-lived pages from the
-		 * on-stack pagepool where pages share among the same request
-		 * and not _all_ inplace I/O pages are needed to be doubled.
-		 */
-		if (!bounced && rq->out[no] == rq->in[ni]) {
-			memcpy(strm->bounce, strm->z.next_in, strm->z.avail_in);
-			strm->z.next_in = strm->bounce;
-			bounced = true;
-		}
-
-		for (j = ni + 1; j < nrpages_in; ++j) {
-			struct page *tmppage;
-
-			if (rq->out[no] != rq->in[j])
-				continue;
-			tmppage = erofs_allocpage(pgpl, rq->gfp);
-			if (!tmppage) {
-				err = -ENOMEM;
-				goto failed;
-			}
-			set_page_private(tmppage, Z_EROFS_SHORTLIVED_PAGE);
-			copy_highpage(tmppage, rq->in[j]);
-			rq->in[j] = tmppage;
-		}
+		dctx.avail_out = strm->z.avail_out;
+		dctx.inbuf_sz = strm->z.avail_in;
+		err = z_erofs_stream_switch_bufs(&dctx,
+					(void **)&strm->z.next_out,
+					(void **)&strm->z.next_in, pgpl);
+		if (err)
+			break;
+		strm->z.avail_out = dctx.avail_out;
+		strm->z.avail_in = dctx.inbuf_sz;
 
 		zerr = zlib_inflate(&strm->z, Z_SYNC_FLUSH);
-		if (zerr != Z_OK || !(outsz + strm->z.avail_out)) {
+		if (zerr != Z_OK || !(rq->outputsize + strm->z.avail_out)) {
 			if (zerr == Z_OK && rq->partial_decoding)
 				break;
-			if (zerr == Z_STREAM_END && !outsz)
+			if (zerr == Z_STREAM_END && !rq->outputsize)
 				break;
 			erofs_err(sb, "failed to decompress %d in[%u] out[%u]",
 				  zerr, rq->inputsize, rq->outputsize);
@@ -237,13 +169,12 @@ again:
 			break;
 		}
 	}
-failed:
 	if (zlib_inflateEnd(&strm->z) != Z_OK && !err)
 		err = -EIO;
-	if (kout)
-		kunmap_local(kout);
+	if (dctx.kout)
+		kunmap_local(dctx.kout);
 failed_zinit:
-	kunmap_local(kin);
+	kunmap_local(dctx.kin);
 	/* 4. push back DEFLATE stream context to the global list */
 	spin_lock(&z_erofs_deflate_lock);
 	strm->next = z_erofs_deflate_head;
@@ -252,3 +183,11 @@ failed_zinit:
 	wake_up(&z_erofs_deflate_wq);
 	return err;
 }
+
+const struct z_erofs_decompressor z_erofs_deflate_decomp = {
+	.config = z_erofs_load_deflate_config,
+	.decompress = z_erofs_deflate_decompress,
+	.init = z_erofs_deflate_init,
+	.exit = z_erofs_deflate_exit,
+	.name = "deflate",
+};
diff --git a/fs/erofs/decompressor_lzma.c b/fs/erofs/decompressor_lzma.c
index 4b28dc130c9f..06a722b85a45 100644
--- a/fs/erofs/decompressor_lzma.c
+++ b/fs/erofs/decompressor_lzma.c
@@ -5,7 +5,6 @@
 struct z_erofs_lzma {
 	struct z_erofs_lzma *next;
 	struct xz_dec_microlzma *state;
-	struct xz_buf buf;
 	u8 bounce[PAGE_SIZE];
 };
 
@@ -18,7 +17,7 @@ static DECLARE_WAIT_QUEUE_HEAD(z_erofs_lzma_wq);
 
 module_param_named(lzma_streams, z_erofs_lzma_nstrms, uint, 0444);
 
-void z_erofs_lzma_exit(void)
+static void z_erofs_lzma_exit(void)
 {
 	/* there should be no running fs instance */
 	while (z_erofs_lzma_avail_strms) {
@@ -46,7 +45,7 @@ void z_erofs_lzma_exit(void)
 	}
 }
 
-int __init z_erofs_lzma_init(void)
+static int __init z_erofs_lzma_init(void)
 {
 	unsigned int i;
 
@@ -70,7 +69,7 @@ int __init z_erofs_lzma_init(void)
 	return 0;
 }
 
-int z_erofs_load_lzma_config(struct super_block *sb,
+static int z_erofs_load_lzma_config(struct super_block *sb,
 			struct erofs_super_block *dsb, void *data, int size)
 {
 	static DEFINE_MUTEX(lzma_resize_mutex);
@@ -147,26 +146,28 @@ again:
 	return err;
 }
 
-int z_erofs_lzma_decompress(struct z_erofs_decompress_req *rq,
-			    struct page **pgpl)
+static int z_erofs_lzma_decompress(struct z_erofs_decompress_req *rq,
+				   struct page **pgpl)
 {
-	const unsigned int nrpages_out =
-		PAGE_ALIGN(rq->pageofs_out + rq->outputsize) >> PAGE_SHIFT;
-	const unsigned int nrpages_in =
-		PAGE_ALIGN(rq->inputsize) >> PAGE_SHIFT;
-	unsigned int inlen, outlen, pageofs;
+	struct super_block *sb = rq->sb;
+	struct z_erofs_stream_dctx dctx = {
+		.rq = rq,
+		.inpages = PAGE_ALIGN(rq->inputsize) >> PAGE_SHIFT,
+		.outpages = PAGE_ALIGN(rq->pageofs_out + rq->outputsize)
+				>> PAGE_SHIFT,
+		.no = -1, .ni = 0,
+	};
+	struct xz_buf buf = {};
 	struct z_erofs_lzma *strm;
-	u8 *kin;
-	bool bounced = false;
-	int no, ni, j, err = 0;
+	enum xz_ret xz_err;
+	int err;
 
 	/* 1. get the exact LZMA compressed size */
-	kin = kmap(*rq->in);
-	err = z_erofs_fixup_insize(rq, kin + rq->pageofs_in,
-			min_t(unsigned int, rq->inputsize,
-			      rq->sb->s_blocksize - rq->pageofs_in));
+	dctx.kin = kmap_local_page(*rq->in);
+	err = z_erofs_fixup_insize(rq, dctx.kin + rq->pageofs_in,
+			min(rq->inputsize, sb->s_blocksize - rq->pageofs_in));
 	if (err) {
-		kunmap(*rq->in);
+		kunmap_local(dctx.kin);
 		return err;
 	}
 
@@ -183,108 +184,45 @@ again:
 	spin_unlock(&z_erofs_lzma_lock);
 
 	/* 3. multi-call decompress */
-	inlen = rq->inputsize;
-	outlen = rq->outputsize;
-	xz_dec_microlzma_reset(strm->state, inlen, outlen,
+	xz_dec_microlzma_reset(strm->state, rq->inputsize, rq->outputsize,
 			       !rq->partial_decoding);
-	pageofs = rq->pageofs_out;
-	strm->buf.in = kin + rq->pageofs_in;
-	strm->buf.in_pos = 0;
-	strm->buf.in_size = min_t(u32, inlen, PAGE_SIZE - rq->pageofs_in);
-	inlen -= strm->buf.in_size;
-	strm->buf.out = NULL;
-	strm->buf.out_pos = 0;
-	strm->buf.out_size = 0;
-
-	for (ni = 0, no = -1;;) {
-		enum xz_ret xz_err;
-
-		if (strm->buf.out_pos == strm->buf.out_size) {
-			if (strm->buf.out) {
-				kunmap(rq->out[no]);
-				strm->buf.out = NULL;
-			}
-
-			if (++no >= nrpages_out || !outlen) {
-				erofs_err(rq->sb, "decompressed buf out of bound");
-				err = -EFSCORRUPTED;
-				break;
-			}
-			strm->buf.out_pos = 0;
-			strm->buf.out_size = min_t(u32, outlen,
-						   PAGE_SIZE - pageofs);
-			outlen -= strm->buf.out_size;
-			if (!rq->out[no] && rq->fillgaps) {	/* deduped */
-				rq->out[no] = erofs_allocpage(pgpl, rq->gfp);
-				if (!rq->out[no]) {
-					err = -ENOMEM;
-					break;
-				}
-				set_page_private(rq->out[no],
-						 Z_EROFS_SHORTLIVED_PAGE);
-			}
-			if (rq->out[no])
-				strm->buf.out = kmap(rq->out[no]) + pageofs;
-			pageofs = 0;
-		} else if (strm->buf.in_pos == strm->buf.in_size) {
-			kunmap(rq->in[ni]);
-
-			if (++ni >= nrpages_in || !inlen) {
-				erofs_err(rq->sb, "compressed buf out of bound");
-				err = -EFSCORRUPTED;
-				break;
-			}
-			strm->buf.in_pos = 0;
-			strm->buf.in_size = min_t(u32, inlen, PAGE_SIZE);
-			inlen -= strm->buf.in_size;
-			kin = kmap(rq->in[ni]);
-			strm->buf.in = kin;
-			bounced = false;
-		}
+	buf.in_size = min(rq->inputsize, PAGE_SIZE - rq->pageofs_in);
+	rq->inputsize -= buf.in_size;
+	buf.in = dctx.kin + rq->pageofs_in,
+	dctx.bounce = strm->bounce;
+	do {
+		dctx.avail_out = buf.out_size - buf.out_pos;
+		dctx.inbuf_sz = buf.in_size;
+		dctx.inbuf_pos = buf.in_pos;
+		err = z_erofs_stream_switch_bufs(&dctx, (void **)&buf.out,
+						 (void **)&buf.in, pgpl);
+		if (err)
+			break;
 
-		/*
-		 * Handle overlapping: Use bounced buffer if the compressed
-		 * data is under processing; Otherwise, Use short-lived pages
-		 * from the on-stack pagepool where pages share with the same
-		 * request.
-		 */
-		if (!bounced && rq->out[no] == rq->in[ni]) {
-			memcpy(strm->bounce, strm->buf.in, strm->buf.in_size);
-			strm->buf.in = strm->bounce;
-			bounced = true;
+		if (buf.out_size == buf.out_pos) {
+			buf.out_size = dctx.avail_out;
+			buf.out_pos = 0;
 		}
-		for (j = ni + 1; j < nrpages_in; ++j) {
-			struct page *tmppage;
+		buf.in_size = dctx.inbuf_sz;
+		buf.in_pos = dctx.inbuf_pos;
 
-			if (rq->out[no] != rq->in[j])
-				continue;
-			tmppage = erofs_allocpage(pgpl, rq->gfp);
-			if (!tmppage) {
-				err = -ENOMEM;
-				goto failed;
-			}
-			set_page_private(tmppage, Z_EROFS_SHORTLIVED_PAGE);
-			copy_highpage(tmppage, rq->in[j]);
-			rq->in[j] = tmppage;
-		}
-		xz_err = xz_dec_microlzma_run(strm->state, &strm->buf);
-		DBG_BUGON(strm->buf.out_pos > strm->buf.out_size);
-		DBG_BUGON(strm->buf.in_pos > strm->buf.in_size);
+		xz_err = xz_dec_microlzma_run(strm->state, &buf);
+		DBG_BUGON(buf.out_pos > buf.out_size);
+		DBG_BUGON(buf.in_pos > buf.in_size);
 
 		if (xz_err != XZ_OK) {
-			if (xz_err == XZ_STREAM_END && !outlen)
+			if (xz_err == XZ_STREAM_END && !rq->outputsize)
 				break;
-			erofs_err(rq->sb, "failed to decompress %d in[%u] out[%u]",
+			erofs_err(sb, "failed to decompress %d in[%u] out[%u]",
 				  xz_err, rq->inputsize, rq->outputsize);
 			err = -EFSCORRUPTED;
 			break;
 		}
-	}
-failed:
-	if (no < nrpages_out && strm->buf.out)
-		kunmap(rq->out[no]);
-	if (ni < nrpages_in)
-		kunmap(rq->in[ni]);
+	} while (1);
+
+	if (dctx.kout)
+		kunmap_local(dctx.kout);
+	kunmap_local(dctx.kin);
 	/* 4. push back LZMA stream context to the global list */
 	spin_lock(&z_erofs_lzma_lock);
 	strm->next = z_erofs_lzma_head;
@@ -293,3 +231,11 @@ failed:
 	wake_up(&z_erofs_lzma_wq);
 	return err;
 }
+
+const struct z_erofs_decompressor z_erofs_lzma_decomp = {
+	.config = z_erofs_load_lzma_config,
+	.decompress = z_erofs_lzma_decompress,
+	.init = z_erofs_lzma_init,
+	.exit = z_erofs_lzma_exit,
+	.name = "lzma"
+};
diff --git a/fs/erofs/decompressor_zstd.c b/fs/erofs/decompressor_zstd.c
index 63a23cac3af4..7e177304967e 100644
--- a/fs/erofs/decompressor_zstd.c
+++ b/fs/erofs/decompressor_zstd.c
@@ -34,7 +34,7 @@ again:
 	return strm;
 }
 
-void z_erofs_zstd_exit(void)
+static void z_erofs_zstd_exit(void)
 {
 	while (z_erofs_zstd_avail_strms) {
 		struct z_erofs_zstd *strm, *n;
@@ -49,7 +49,7 @@ void z_erofs_zstd_exit(void)
 	}
 }
 
-int __init z_erofs_zstd_init(void)
+static int __init z_erofs_zstd_init(void)
 {
 	/* by default, use # of possible CPUs instead */
 	if (!z_erofs_zstd_nstrms)
@@ -72,7 +72,7 @@ int __init z_erofs_zstd_init(void)
 	return 0;
 }
 
-int z_erofs_load_zstd_config(struct super_block *sb,
+static int z_erofs_load_zstd_config(struct super_block *sb,
 			struct erofs_super_block *dsb, void *data, int size)
 {
 	static DEFINE_MUTEX(zstd_resize_mutex);
@@ -135,30 +135,29 @@ int z_erofs_load_zstd_config(struct super_block *sb,
 	return strm ? -ENOMEM : 0;
 }
 
-int z_erofs_zstd_decompress(struct z_erofs_decompress_req *rq,
-			    struct page **pgpl)
+static int z_erofs_zstd_decompress(struct z_erofs_decompress_req *rq,
+				   struct page **pgpl)
 {
-	const unsigned int nrpages_out =
-		PAGE_ALIGN(rq->pageofs_out + rq->outputsize) >> PAGE_SHIFT;
-	const unsigned int nrpages_in =
-		PAGE_ALIGN(rq->inputsize) >> PAGE_SHIFT;
-	zstd_dstream *stream;
 	struct super_block *sb = rq->sb;
-	unsigned int insz, outsz, pofs;
-	struct z_erofs_zstd *strm;
+	struct z_erofs_stream_dctx dctx = {
+		.rq = rq,
+		.inpages = PAGE_ALIGN(rq->inputsize) >> PAGE_SHIFT,
+		.outpages = PAGE_ALIGN(rq->pageofs_out + rq->outputsize)
+				>> PAGE_SHIFT,
+		.no = -1, .ni = 0,
+	};
 	zstd_in_buffer in_buf = { NULL, 0, 0 };
 	zstd_out_buffer out_buf = { NULL, 0, 0 };
-	u8 *kin, *kout = NULL;
-	bool bounced = false;
-	int no = -1, ni = 0, j = 0, zerr, err;
+	struct z_erofs_zstd *strm;
+	zstd_dstream *stream;
+	int zerr, err;
 
 	/* 1. get the exact compressed size */
-	kin = kmap_local_page(*rq->in);
-	err = z_erofs_fixup_insize(rq, kin + rq->pageofs_in,
-			min_t(unsigned int, rq->inputsize,
-			      sb->s_blocksize - rq->pageofs_in));
+	dctx.kin = kmap_local_page(*rq->in);
+	err = z_erofs_fixup_insize(rq, dctx.kin + rq->pageofs_in,
+			min(rq->inputsize, sb->s_blocksize - rq->pageofs_in));
 	if (err) {
-		kunmap_local(kin);
+		kunmap_local(dctx.kin);
 		return err;
 	}
 
@@ -166,109 +165,48 @@ int z_erofs_zstd_decompress(struct z_erofs_decompress_req *rq,
 	strm = z_erofs_isolate_strms(false);
 
 	/* 3. multi-call decompress */
-	insz = rq->inputsize;
-	outsz = rq->outputsize;
 	stream = zstd_init_dstream(z_erofs_zstd_max_dictsize, strm->wksp, strm->wkspsz);
 	if (!stream) {
 		err = -EIO;
 		goto failed_zinit;
 	}
 
-	pofs = rq->pageofs_out;
-	in_buf.size = min_t(u32, insz, PAGE_SIZE - rq->pageofs_in);
-	insz -= in_buf.size;
-	in_buf.src = kin + rq->pageofs_in;
+	rq->fillgaps = true;	/* ZSTD doesn't support NULL output buffer */
+	in_buf.size = min_t(u32, rq->inputsize, PAGE_SIZE - rq->pageofs_in);
+	rq->inputsize -= in_buf.size;
+	in_buf.src = dctx.kin + rq->pageofs_in;
+	dctx.bounce = strm->bounce;
+
 	do {
-		if (out_buf.size == out_buf.pos) {
-			if (++no >= nrpages_out || !outsz) {
-				erofs_err(sb, "insufficient space for decompressed data");
-				err = -EFSCORRUPTED;
-				break;
-			}
+		dctx.avail_out = out_buf.size - out_buf.pos;
+		dctx.inbuf_sz = in_buf.size;
+		dctx.inbuf_pos = in_buf.pos;
+		err = z_erofs_stream_switch_bufs(&dctx, &out_buf.dst,
+						 (void **)&in_buf.src, pgpl);
+		if (err)
+			break;
 
-			if (kout)
-				kunmap_local(kout);
-			out_buf.size = min_t(u32, outsz, PAGE_SIZE - pofs);
-			outsz -= out_buf.size;
-			if (!rq->out[no]) {
-				rq->out[no] = erofs_allocpage(pgpl, rq->gfp);
-				if (!rq->out[no]) {
-					kout = NULL;
-					err = -ENOMEM;
-					break;
-				}
-				set_page_private(rq->out[no],
-						 Z_EROFS_SHORTLIVED_PAGE);
-			}
-			kout = kmap_local_page(rq->out[no]);
-			out_buf.dst = kout + pofs;
+		if (out_buf.size == out_buf.pos) {
+			out_buf.size = dctx.avail_out;
 			out_buf.pos = 0;
-			pofs = 0;
-		}
-
-		if (in_buf.size == in_buf.pos && insz) {
-			if (++ni >= nrpages_in) {
-				erofs_err(sb, "invalid compressed data");
-				err = -EFSCORRUPTED;
-				break;
-			}
-
-			if (kout) /* unlike kmap(), take care of the orders */
-				kunmap_local(kout);
-			kunmap_local(kin);
-			in_buf.size = min_t(u32, insz, PAGE_SIZE);
-			insz -= in_buf.size;
-			kin = kmap_local_page(rq->in[ni]);
-			in_buf.src = kin;
-			in_buf.pos = 0;
-			bounced = false;
-			if (kout) {
-				j = (u8 *)out_buf.dst - kout;
-				kout = kmap_local_page(rq->out[no]);
-				out_buf.dst = kout + j;
-			}
 		}
+		in_buf.size = dctx.inbuf_sz;
+		in_buf.pos = dctx.inbuf_pos;
 
-		/*
-		 * Handle overlapping: Use bounced buffer if the compressed
-		 * data is under processing; Or use short-lived pages from the
-		 * on-stack pagepool where pages share among the same request
-		 * and not _all_ inplace I/O pages are needed to be doubled.
-		 */
-		if (!bounced && rq->out[no] == rq->in[ni]) {
-			memcpy(strm->bounce, in_buf.src, in_buf.size);
-			in_buf.src = strm->bounce;
-			bounced = true;
-		}
-
-		for (j = ni + 1; j < nrpages_in; ++j) {
-			struct page *tmppage;
-
-			if (rq->out[no] != rq->in[j])
-				continue;
-			tmppage = erofs_allocpage(pgp