+ zram-cond_resched-in-writeback-loop.patch added to mm-unstable branch

+ zram-cond_resched-in-writeback-loop.patch added to mm-unstable branch

[Andrew Morton]

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

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Sergey Senozhatsky <senozhatsky@chromium.org>
Subject: zram: cond_resched() in writeback loop
Date: Tue, 10 Dec 2024 19:53:55 +0900

Patch series "zram: split page type read/write handling".

This is a subset of [1] series which contains only fixes and improvements
(no new features, as ZRAM_HUGE split is still under consideration).

The motivation for factoring out is that zram_write_page() gets more and
more complex all the time, because it tries to handle too many scenarios:
ZRAM_SAME store, ZRAM_HUGE store, compress page store with zs_malloc
allocation slowpath and conditional recompression, etc.  Factor those out
and make things easier to handle.

Addition of cond_resched() is simply a fix, I can trigger watchdog from
zram writeback().  And early slot free is just a reasonable thing to do.

[1] https://lore.kernel.org/linux-kernel/20241119072057.3440039-1-senozhatsky@chromium.org


This patch (of 6):

Writeback loop can run for quite a while (depending on wb device
performance, compression algorithm and the number of entries we
writeback), so we need to do cond_resched() there, similarly to what we do
in recompress loop.

Link: https://lkml.kernel.org/r/20241210105420.1888790-1-senozhatsky@chromium.org
Link: https://lkml.kernel.org/r/20241210105420.1888790-2-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 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
@@ -889,6 +889,8 @@ 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@chromium.org are

zram-panic-when-use-ext4-over-zram-fix.patch
zram-cond_resched-in-writeback-loop.patch
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-cond_resched-in-writeback-loop.patch added to mm-unstable branch

[Andrew Morton]

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

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Sergey Senozhatsky <senozhatsky@chromium.org>
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@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 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@chromium.org 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