From b0377ee8042985b0d91bf579afcc4ee9150db14d Mon Sep 17 00:00:00 2001 From: Sergey Senozhatsky Date: Thu, 19 Mar 2026 12:44:56 +0900 Subject: zram: do not slot_free() written-back slots 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: d38fab605c667 ("zram: introduce compressed data writeback") Signed-off-by: Sergey Senozhatsky Acked-by: Minchan Kim Cc: Brian Geffon Cc: Richard Chang Signed-off-by: Andrew Morton --- drivers/block/zram/zram_drv.c | 39 ++++++++++++++------------------------- 1 file changed, 14 insertions(+), 25 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index a324ede6206d..af679375b193 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -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)) { -- cgit v1.2.3