[PATCH 09/10] erofs: support unaligned encoded data

From: Gao Xiang
Date: Mon Mar 10 2025 - 05:56:45 EST

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We're almost there. It's straight-forward to adapt the current
decompression subsystem to support unaligned encoded (compressed) data.

Note that unaligned data is not encouraged because of worse I/O and
caching efficiency unless the corresponding compressor doesn't support
fixed-sized output compression natively like Zstd.

Signed-off-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>
---
fs/erofs/decompressor.c | 2 +-
fs/erofs/zdata.c | 92 ++++++++++++++++++++---------------------
2 files changed, 46 insertions(+), 48 deletions(-)

diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
index 50e350b10f89..bf62e2836b60 100644
--- a/fs/erofs/decompressor.c
+++ b/fs/erofs/decompressor.c
@@ -313,7 +313,7 @@ static int z_erofs_transform_plain(struct z_erofs_decompress_req *rq,
rq->outputsize -= cur;
}

- for (; rq->outputsize; rq->pageofs_in = 0, cur += PAGE_SIZE, ni++) {
+ for (; rq->outputsize; rq->pageofs_in = 0, cur += insz, ni++) {
insz = min(PAGE_SIZE - rq->pageofs_in, rq->outputsize);
rq->outputsize -= insz;
if (!rq->in[ni])
diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index bc6d6842c5c2..0671184d9cf1 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -44,8 +44,8 @@ struct z_erofs_pcluster {
/* A: point to next chained pcluster or TAILs */
struct z_erofs_pcluster *next;

- /* I: start block address of this pcluster */
- erofs_off_t index;
+ /* I: start physical position of this pcluster */
+ erofs_off_t pos;

/* L: the maximum decompression size of this round */
unsigned int length;
@@ -73,6 +73,9 @@ struct z_erofs_pcluster {
/* I: compression algorithm format */
unsigned char algorithmformat;

+ /* I: whether compressed data is in-lined or not */
+ bool from_meta;
+
/* L: whether partial decompression or not */
bool partial;

@@ -102,14 +105,9 @@ struct z_erofs_decompressqueue {
bool eio, sync;
};

-static inline bool z_erofs_is_inline_pcluster(struct z_erofs_pcluster *pcl)
-{
- return !pcl->index;
-}
-
static inline unsigned int z_erofs_pclusterpages(struct z_erofs_pcluster *pcl)
{
- return PAGE_ALIGN(pcl->pclustersize) >> PAGE_SHIFT;
+ return PAGE_ALIGN(pcl->pageofs_in + pcl->pclustersize) >> PAGE_SHIFT;
}

static bool erofs_folio_is_managed(struct erofs_sb_info *sbi, struct folio *fo)
@@ -133,7 +131,7 @@ struct z_erofs_pcluster_slab {

static struct z_erofs_pcluster_slab pcluster_pool[] __read_mostly = {
_PCLP(1), _PCLP(4), _PCLP(16), _PCLP(64), _PCLP(128),
- _PCLP(Z_EROFS_PCLUSTER_MAX_PAGES)
+ _PCLP(Z_EROFS_PCLUSTER_MAX_PAGES + 1)
};

struct z_erofs_bvec_iter {
@@ -267,7 +265,6 @@ static struct z_erofs_pcluster *z_erofs_alloc_pcluster(unsigned int size)
pcl = kmem_cache_zalloc(pcs->slab, GFP_KERNEL);
if (!pcl)
return ERR_PTR(-ENOMEM);
- pcl->pclustersize = size;
return pcl;
}
return ERR_PTR(-EINVAL);
@@ -516,6 +513,7 @@ static void z_erofs_bind_cache(struct z_erofs_frontend *fe)
struct z_erofs_pcluster *pcl = fe->pcl;
unsigned int pclusterpages = z_erofs_pclusterpages(pcl);
bool shouldalloc = z_erofs_should_alloc_cache(fe);
+ pgoff_t poff = pcl->pos >> PAGE_SHIFT;
bool may_bypass = true;
/* Optimistic allocation, as in-place I/O can be used as a fallback */
gfp_t gfp = (mapping_gfp_mask(mc) & ~__GFP_DIRECT_RECLAIM) |
@@ -532,7 +530,7 @@ static void z_erofs_bind_cache(struct z_erofs_frontend *fe)
if (READ_ONCE(pcl->compressed_bvecs[i].page))
continue;

- folio = filemap_get_folio(mc, pcl->index + i);
+ folio = filemap_get_folio(mc, poff + i);
if (IS_ERR(folio)) {
may_bypass = false;
if (!shouldalloc)
@@ -575,7 +573,7 @@ static int erofs_try_to_free_all_cached_folios(struct erofs_sb_info *sbi,
struct folio *folio;
int i;

- DBG_BUGON(z_erofs_is_inline_pcluster(pcl));
+ DBG_BUGON(pcl->from_meta);
/* Each cached folio contains one page unless bs > ps is supported */
for (i = 0; i < pclusterpages; ++i) {
if (pcl->compressed_bvecs[i].page) {
@@ -607,7 +605,7 @@ static bool z_erofs_cache_release_folio(struct folio *folio, gfp_t gfp)
ret = false;
spin_lock(&pcl->lockref.lock);
if (pcl->lockref.count <= 0) {
- DBG_BUGON(z_erofs_is_inline_pcluster(pcl));
+ DBG_BUGON(pcl->from_meta);
for (; bvec < end; ++bvec) {
if (bvec->page && page_folio(bvec->page) == folio) {
bvec->page = NULL;
@@ -667,16 +665,20 @@ static int z_erofs_attach_page(struct z_erofs_frontend *fe,
int ret;

if (exclusive) {
- /* give priority for inplaceio to use file pages first */
- spin_lock(&pcl->lockref.lock);
- while (fe->icur > 0) {
- if (pcl->compressed_bvecs[--fe->icur].page)
- continue;
- pcl->compressed_bvecs[fe->icur] = *bvec;
+ /* Inplace I/O is limited to one page for uncompressed data */
+ if (pcl->algorithmformat < Z_EROFS_COMPRESSION_MAX ||
+ fe->icur <= 1) {
+ /* Try to prioritize inplace I/O here */
+ spin_lock(&pcl->lockref.lock);
+ while (fe->icur > 0) {
+ if (pcl->compressed_bvecs[--fe->icur].page)
+ continue;
+ pcl->compressed_bvecs[fe->icur] = *bvec;
+ spin_unlock(&pcl->lockref.lock);
+ return 0;
+ }
spin_unlock(&pcl->lockref.lock);
- return 0;
}
- spin_unlock(&pcl->lockref.lock);

/* otherwise, check if it can be used as a bvpage */
if (fe->mode >= Z_EROFS_PCLUSTER_FOLLOWED &&
@@ -711,27 +713,26 @@ static int z_erofs_register_pcluster(struct z_erofs_frontend *fe)
struct erofs_map_blocks *map = &fe->map;
struct super_block *sb = fe->inode->i_sb;
struct erofs_sb_info *sbi = EROFS_SB(sb);
- bool ztailpacking = map->m_flags & EROFS_MAP_META;
struct z_erofs_pcluster *pcl, *pre;
+ unsigned int pageofs_in;
int err;

- if (!(map->m_flags & EROFS_MAP_ENCODED) ||
- (!ztailpacking && !erofs_blknr(sb, map->m_pa))) {
- DBG_BUGON(1);
- return -EFSCORRUPTED;
- }
-
- /* no available pcluster, let's allocate one */
- pcl = z_erofs_alloc_pcluster(map->m_plen);
+ pageofs_in = erofs_blkoff(sb, map->m_pa);
+ pcl = z_erofs_alloc_pcluster(pageofs_in + map->m_plen);
if (IS_ERR(pcl))
return PTR_ERR(pcl);

lockref_init(&pcl->lockref); /* one ref for this request */
pcl->algorithmformat = map->m_algorithmformat;
+ pcl->pclustersize = map->m_plen;
+ pcl->pageofs_in = pageofs_in;
pcl->length = 0;
pcl->partial = true;
pcl->next = fe->head;
+ pcl->pos = map->m_pa;
+ pcl->pageofs_in = pageofs_in;
pcl->pageofs_out = map->m_la & ~PAGE_MASK;
+ pcl->from_meta = map->m_flags & EROFS_MAP_META;
fe->mode = Z_EROFS_PCLUSTER_FOLLOWED;

/*
@@ -741,13 +742,10 @@ static int z_erofs_register_pcluster(struct z_erofs_frontend *fe)
mutex_init(&pcl->lock);
DBG_BUGON(!mutex_trylock(&pcl->lock));

- if (ztailpacking) {
- pcl->index = 0; /* which indicates ztailpacking */
- } else {
- pcl->index = erofs_blknr(sb, map->m_pa);
+ if (!pcl->from_meta) {
while (1) {
xa_lock(&sbi->managed_pslots);
- pre = __xa_cmpxchg(&sbi->managed_pslots, pcl->index,
+ pre = __xa_cmpxchg(&sbi->managed_pslots, pcl->pos,
NULL, pcl, GFP_KERNEL);
if (!pre || xa_is_err(pre) || z_erofs_get_pcluster(pre)) {
xa_unlock(&sbi->managed_pslots);
@@ -779,7 +777,6 @@ static int z_erofs_pcluster_begin(struct z_erofs_frontend *fe)
{
struct erofs_map_blocks *map = &fe->map;
struct super_block *sb = fe->inode->i_sb;
- erofs_blk_t blknr = erofs_blknr(sb, map->m_pa);
struct z_erofs_pcluster *pcl = NULL;
int ret;

@@ -790,9 +787,9 @@ static int z_erofs_pcluster_begin(struct z_erofs_frontend *fe)
if (!(map->m_flags & EROFS_MAP_META)) {
while (1) {
rcu_read_lock();
- pcl = xa_load(&EROFS_SB(sb)->managed_pslots, blknr);
+ pcl = xa_load(&EROFS_SB(sb)->managed_pslots, map->m_pa);
if (!pcl || z_erofs_get_pcluster(pcl)) {
- DBG_BUGON(pcl && blknr != pcl->index);
+ DBG_BUGON(pcl && map->m_pa != pcl->pos);
rcu_read_unlock();
break;
}
@@ -826,7 +823,7 @@ static int z_erofs_pcluster_begin(struct z_erofs_frontend *fe)

z_erofs_bvec_iter_begin(&fe->biter, &fe->pcl->bvset,
Z_EROFS_INLINE_BVECS, fe->pcl->vcnt);
- if (!z_erofs_is_inline_pcluster(fe->pcl)) {
+ if (!fe->pcl->from_meta) {
/* bind cache first when cached decompression is preferred */
z_erofs_bind_cache(fe);
} else {
@@ -871,7 +868,7 @@ static bool __erofs_try_to_release_pcluster(struct erofs_sb_info *sbi,
* It's impossible to fail after the pcluster is freezed, but in order
* to avoid some race conditions, add a DBG_BUGON to observe this.
*/
- DBG_BUGON(__xa_erase(&sbi->managed_pslots, pcl->index) != pcl);
+ DBG_BUGON(__xa_erase(&sbi->managed_pslots, pcl->pos) != pcl);

lockref_mark_dead(&pcl->lockref);
return true;
@@ -1221,7 +1218,7 @@ static int z_erofs_parse_in_bvecs(struct z_erofs_backend *be, bool *overlapped)
}
be->compressed_pages[i] = page;

- if (z_erofs_is_inline_pcluster(pcl) ||
+ if (pcl->from_meta ||
erofs_folio_is_managed(EROFS_SB(be->sb), page_folio(page))) {
if (!PageUptodate(page))
err = -EIO;
@@ -1299,7 +1296,7 @@ static int z_erofs_decompress_pcluster(struct z_erofs_backend *be, int err)
}, be->pagepool);

/* must handle all compressed pages before actual file pages */
- if (z_erofs_is_inline_pcluster(pcl)) {
+ if (pcl->from_meta) {
page = pcl->compressed_bvecs[0].page;
WRITE_ONCE(pcl->compressed_bvecs[0].page, NULL);
put_page(page);
@@ -1359,7 +1356,7 @@ static int z_erofs_decompress_pcluster(struct z_erofs_backend *be, int err)
WRITE_ONCE(pcl->next, NULL);
mutex_unlock(&pcl->lock);

- if (z_erofs_is_inline_pcluster(pcl))
+ if (pcl->from_meta)
z_erofs_free_pcluster(pcl);
else
z_erofs_put_pcluster(sbi, pcl, try_free);
@@ -1540,7 +1537,7 @@ static void z_erofs_fill_bio_vec(struct bio_vec *bvec,
folio = page_folio(page);
out_tocache:
if (!tocache || bs != PAGE_SIZE ||
- filemap_add_folio(mc, folio, pcl->index + nr, gfp)) {
+ filemap_add_folio(mc, folio, (pcl->pos >> PAGE_SHIFT) + nr, gfp)) {
/* turn into a temporary shortlived folio (1 ref) */
folio->private = (void *)Z_EROFS_SHORTLIVED_PAGE;
return;
@@ -1657,19 +1654,20 @@ static void z_erofs_submit_queue(struct z_erofs_frontend *f,

pcl = next;
next = READ_ONCE(pcl->next);
- if (z_erofs_is_inline_pcluster(pcl)) {
+ if (pcl->from_meta) {
z_erofs_move_to_bypass_queue(pcl, next, qtail);
continue;
}

/* no device id here, thus it will always succeed */
mdev = (struct erofs_map_dev) {
- .m_pa = erofs_pos(sb, pcl->index),
+ .m_pa = round_down(pcl->pos, sb->s_blocksize),
};
(void)erofs_map_dev(sb, &mdev);

cur = mdev.m_pa;
- end = cur + pcl->pclustersize;
+ end = round_up(cur + pcl->pageofs_in + pcl->pclustersize,
+ sb->s_blocksize);
do {
bvec.bv_page = NULL;
if (bio && (cur != last_pa ||
--
2.43.5

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Previous message: Gao Xiang: "[PATCH 07/10] erofs: add encoded extent on-disk definition"
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