From: Kairui Song <ryncsn@gmail.com>
To: Zi Yan <ziy@nvidia.com>
Cc: Shivam Kalra <shivamkalra98@zohomail.in>,
Kairui Song <kasong@tencent.com>,
Andrew Morton <akpm@linux-foundation.org>,
David Hildenbrand <david@kernel.org>,
Lorenzo Stoakes <ljs@kernel.org>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
"Liam R. Howlett" <liam@infradead.org>,
Ryan Roberts <ryan.roberts@arm.com>, Dev Jain <dev.jain@arm.com>,
Barry Song <baohua@kernel.org>,
Lance Yang <lance.yang@linux.dev>,
Usama Arif <usama.arif@linux.dev>,
Vlastimil Babka <vbabka@kernel.org>,
Mike Rapoport <rppt@kernel.org>,
Suren Baghdasaryan <surenb@google.com>,
Michal Hocko <mhocko@suse.com>, Shuah Khan <shuah@kernel.org>,
Nico Pache <nico.pache@linux.dev>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linux-kselftest@vger.kernel.org
Subject: Re: [PATCH 0/3] mm: support splitting mappingless swapcache folios
Date: Sat, 8 Aug 2026 05:22:41 +0800 [thread overview]
Message-ID: <anZLkwwxHdhM2M2Q@KASONG-MC4> (raw)
In-Reply-To: <DKIRYOJXLIYN.32KI06POZL7SY@nvidia.com>
On Fri, Aug 07, 2026 at 10:18:05AM +0800, Zi Yan wrote:
> On Wed Aug 5, 2026 at 11:54 AM EDT, Kairui Song wrote:
> > On Wed, Aug 05, 2026 at 08:03:33AM +0800, Zi Yan wrote:
> >> On 5 Aug 2026, at 7:18, Shivam Kalra via B4 Relay wrote:
> >>
> >> > Large shmem folios lose their address-space mapping when they are written
> >> > to swap, but remain valid members of the swap cache. Folios read from swap
> >> > but not yet associated with an anon_vma can have the same mappingless
> >> > swapcache state. folio_check_splittable() currently mistakes both cases for
> >> > truncation and rejects the split with -EBUSY.
> >> >
> >> > Implement the longstanding TODO for this state. Allow mappingless
> >> > swapcache folios to use the existing uniform order-0 swapcache split path,
> >> > while continuing to reject truly truncated folios and unsupported
> >> > higher-order or non-uniform swapcache splits.
> >>
> >> Thank you for your patches.
> >>
> >> As Kairui (cc’d) mentioned in [1] (see “A bit more details on this”),
> >> we might not need to implement this split. I will let Kairui to decide
> >> how we should deal with this patchset.
> >>
> >> [1] https://lore.kernel.org/all/CAMgjq7CHDG8JhesSPMkn1kzG8jKb0BXO756BvxMQC_MCn2eTyA@mail.gmail.com/
> >
> > Thanks for the CC, this is actually not hard to implement as shown by
> > Shivam, I just found the code more and more hard to follow and fragile
> > as we add more logic to it. And we don't have to reject higher order
> > split either which can be seen easily if the code is cleaner.
> >
> > Personally I think doing some cleanup first is better, I haven't post any
> > code as right now there doesn't seem to be much user of this. It will be
> > needed if more clean THP swapcache begin to show up due to things like
> > THP readahead for swap, which isn't here yet. I think I can send an RFC
> > tomorrow just for reference. I'm fine if we prefer to remove that TODO
> > using this smaller change first :)
>
> Thanks. Can you also help review this patchset? The changes looks good
> to me but I am not sure if I get all the details about swapcache handling.
>
> --
> Best Regards,
> Yan, Zi
Hello,
Thanks for the reminder, I got a bit busy so delayed for a day on that
RFC.
For this series I think it's functionally fine, just the split logic is
a bit complex to follow and we still have restriction on swap cache
for order 0 uniform split only. I'll have a closer look later. Also
let me know how you think about that RFC.
prev parent reply other threads:[~2026-08-07 21:22 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-05 11:18 [PATCH 0/3] mm: support splitting mappingless swapcache folios Shivam Kalra via B4 Relay
2026-08-05 11:18 ` [PATCH 1/3] mm/huge_memory: allow " Shivam Kalra via B4 Relay
2026-08-05 11:18 ` [PATCH 2/3] mm: add KUnit coverage for " Shivam Kalra via B4 Relay
2026-08-05 11:18 ` [PATCH 3/3] selftests/mm: test hwpoison recovery of mappingless swapcache THPs Shivam Kalra via B4 Relay
2026-08-05 12:03 ` [PATCH 0/3] mm: support splitting mappingless swapcache folios Zi Yan
2026-08-05 15:54 ` Kairui Song
2026-08-07 14:18 ` Zi Yan
2026-08-07 21:22 ` Kairui Song [this message]
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