On 1/28/25 19:18, Hyeonggon Yoo wrote:
> On Tue, Jan 28, 2025 at 6:14 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>>
>> On Wed, Jan 29, 2025 at 02:49:38AM +0900, Hyeonggon Yoo wrote:
>> > Commit b7c0ccdfbafd ("mm: zswap: support large folios in zswap_store()")
>> > mistakenly skipped charging any zswapped pages when a single call to
>> > zswap_store_page() failed, even if some pages in the folio are
>> > successfully stored in zswap.
>> >
>> > Making things worse, these not-charged pages are uncharged in
>> > zswap_entry_free(), making zswap charging inconsistent.
>> >
>> > This inconsistency triggers two warnings when following these steps:
>> > # On a machine with 64GiB of RAM and 36GiB of zswap
>> > $ stress-ng --bigheap 2 # wait until the OOM-killer kills stress-ng
>> > $ sudo reboot
>> >
>> > Two warnings are:
>> > in mm/memcontrol.c:163, function obj_cgroup_release():
>> > WARN_ON_ONCE(nr_bytes & (PAGE_SIZE - 1));
>> >
>> > in mm/page_counter.c:60, function page_counter_cancel():
>> > if (WARN_ONCE(new < 0, "page_counter underflow: %ld nr_pages=%lu\n",
>> > new, nr_pages))
>> >
>> > Charge zswapped pages even if some pages of the folio are not zswapped.
>> > After resolving the inconsistency, these warnings disappear.
>> >
>> > Fixes: b7c0ccdfbafd ("mm: zswap: support large folios in zswap_store()")
>>
>> This commit is in 6.13, not 6.12, so your subject line is a bit
>> confusing :(
>
> Oh, thanks for catching. Will fix it.
> Also, I noticed I incorrectly described the problem.
>
> Will send v2 (for v6.13!) after adjusting them.
I think we use e.g. "v6.13 hotfix" only while the stabilization of 6.13 is
ongoing, to indicate the urgency. Now it's too late so it would only confuse
stable maintainers, while the patch is not directly aimed at stable, but
through mm to mainline and then stable backport as usual. So I think you can
just use [PATCH mm-hotfixes] at this point.
> Best,
> Hyeonggon
>
