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zram: do not slot_free() written-back slots

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slot_free() basically completely resets the slots by clearing all of
its flags and attributes.  While zram_writeback_complete() restores
some of flags back (those that are necessary for async read
decompression) we still lose a lot of slot's metadata.  For example,
slot's ac-time, or ZRAM_INCOMPRESSIBLE.

More importantly, restoring flags/attrs requires extra attention as
some of the flags are directly affecting zram device stats.  And the
original code did not pay that attention.  Namely ZRAM_HUGE slots
handling in zram_writeback_complete().  The call to slot_free() would
decrement ->huge_pages, however when zram_writeback_complete() restored
the slot's ZRAM_HUGE flag, it would not get reflected in an incremented
->huge_pages.  So when the slot would finally get freed, slot_free()
would decrement ->huge_pages again, leading to underflow.

Fix this by open-coding the required memory free and stats updates in
zram_writeback_complete(), rather than calling the destructive
slot_free().  Since we now preserve the ZRAM_HUGE flag on written-back
slots (for the deferred decompression path), we also update slot_free()
to skip decrementing ->huge_pages if ZRAM_WB is set.

Link: https://lkml.kernel.org/r/20260320023143.2372879-1-senozhatsky@chromium.org
Link: https://lkml.kernel.org/r/20260319034912.1894770-1-senozhatsky@chromium.org
Fixes: d38fab605c ("zram: introduce compressed data writeback")
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Richard Chang <richardycc@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Sergey Senozhatsky
2026-03-19 12:44:56 +09:00
committed by Andrew Morton
parent 26f775a054
commit b0377ee804
1 changed files with 14 additions and 25 deletions
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39
drivers/block/zram/zram_drv.c
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@@ -917,9 +917,8 @@ static void zram_account_writeback_submit(struct zram *zram)
static int zram_writeback_complete(struct zram *zram, struct zram_wb_req *req)
{
u32 size, index = req->pps->index;
int err, prio;
bool huge;
u32 index = req->pps->index;
int err;
err = blk_status_to_errno(req->bio.bi_status);
if (err) {
@@ -946,28 +945,13 @@ static int zram_writeback_complete(struct zram *zram, struct zram_wb_req *req)
goto out;
}
if (zram->compressed_wb) {
/*
* ZRAM_WB slots get freed, we need to preserve data required
* for read decompression.
*/
size = get_slot_size(zram, index);
prio = get_slot_comp_priority(zram, index);
huge = test_slot_flag(zram, index, ZRAM_HUGE);
}
slot_free(zram, index);
set_slot_flag(zram, index, ZRAM_WB);
clear_slot_flag(zram, index, ZRAM_IDLE);
if (test_slot_flag(zram, index, ZRAM_HUGE))
atomic64_dec(&zram->stats.huge_pages);
atomic64_sub(get_slot_size(zram, index), &zram->stats.compr_data_size);
zs_free(zram->mem_pool, get_slot_handle(zram, index));
set_slot_handle(zram, index, req->blk_idx);
if (zram->compressed_wb) {
if (huge)
set_slot_flag(zram, index, ZRAM_HUGE);
set_slot_size(zram, index, size);
set_slot_comp_priority(zram, index, prio);
}
atomic64_inc(&zram->stats.pages_stored);
set_slot_flag(zram, index, ZRAM_WB);
out:
slot_unlock(zram, index);
@@ -2010,8 +1994,13 @@ static void slot_free(struct zram *zram, u32 index)
set_slot_comp_priority(zram, index, 0);
if (test_slot_flag(zram, index, ZRAM_HUGE)) {
/*
* Writeback completion decrements ->huge_pages but keeps
* ZRAM_HUGE flag for deferred decompression path.
*/
if (!test_slot_flag(zram, index, ZRAM_WB))
atomic64_dec(&zram->stats.huge_pages);
clear_slot_flag(zram, index, ZRAM_HUGE);
atomic64_dec(&zram->stats.huge_pages);
}
if (test_slot_flag(zram, index, ZRAM_WB)) {