The patch titled
Subject: zram: cond_resched() in writeback loop
has been added to the -mm mm-unstable branch. Its filename is
zram-cond_resched-in-writeback-loop.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/zram-cond_resched-in-writeback-loop.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
Subject: zram: cond_resched() in writeback loop
Date: Wed, 18 Dec 2024 15:34:24 +0900
zram writeback is a costly operation, because every target slot (unless
ZRAM_HUGE) is decompressed before it gets written to a backing device.
The writeback to a backing device uses submit_bio_wait() which may look
like a rescheduling point. However, if the backing device has
BD_HAS_SUBMIT_BIO bit set __submit_bio() calls directly
disk->fops->submit_bio(bio) on the backing device and so when
submit_bio_wait() calls blk_wait_io() the I/O is already done. On such
systems we effective end up in a loop
for_each (target slot) {
decompress(slot)
__submit_bio()
disk->fops->submit_bio(bio)
}
Which on PREEMPT_NONE systems triggers watchdogs (since there are no
explicit rescheduling points). Add cond_resched() to the zram writeback
loop.
Link: https://lkml.kernel.org/r/20241218063513.297475-8-senozhatsky@xxxxxxxxxxxx
Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/block/zram/zram_drv.c | 2 ++
1 file changed, 2 insertions(+)
--- a/drivers/block/zram/zram_drv.c~zram-cond_resched-in-writeback-loop
+++ a/drivers/block/zram/zram_drv.c
@@ -884,6 +884,8 @@ static ssize_t writeback_store(struct de
next:
zram_slot_unlock(zram, index);
release_pp_slot(zram, pps);
+
+ cond_resched();
}
if (blk_idx)
_
Patches currently in -mm which might be from senozhatsky@xxxxxxxxxxxx are
zram-free-slot-memory-early-during-write.patch
zram-remove-entry-element-member.patch
zram-factor-out-zram_same-write.patch
zram-factor-out-zram_huge-write.patch
zram-factor-out-different-page-types-read.patch
zram-use-zram_read_from_zspool-in-writeback.patch
zram-cond_resched-in-writeback-loop.patch
