linux-kernel - Re: [PATCH v4 00/15] mm, swap: introduce swap table as swap cache (phase I)

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Message-ID: <99f57a96-611a-b6be-fe00-3ac785154d1c@google.com>
Date: Tue, 16 Sep 2025 14:22:51 -0700 (PDT)
From: Hugh Dickins <hughd@...gle.com>
To: Kairui Song <ryncsn@...il.com>
cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>, 
    Matthew Wilcox <willy@...radead.org>, Hugh Dickins <hughd@...gle.com>, 
    Chris Li <chrisl@...nel.org>, Barry Song <baohua@...nel.org>, 
    Baoquan He <bhe@...hat.com>, Nhat Pham <nphamcs@...il.com>, 
    Kemeng Shi <shikemeng@...weicloud.com>, 
    Baolin Wang <baolin.wang@...ux.alibaba.com>, 
    Ying Huang <ying.huang@...ux.alibaba.com>, 
    Johannes Weiner <hannes@...xchg.org>, David Hildenbrand <david@...hat.com>, 
    Yosry Ahmed <yosryahmed@...gle.com>, 
    Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Zi Yan <ziy@...dia.com>, 
    linux-kernel@...r.kernel.org, Kairui Song <kasong@...cent.com>
Subject: Re: [PATCH v4 00/15] mm, swap: introduce swap table as swap cache
 (phase I)

On Wed, 17 Sep 2025, Kairui Song wrote:
> V4 changes:
> - Patch 14: fix potential cluster leak when attemp a sleep allocation of
>   swap table: Just remove the logic that check and return the percpu
>   cluster, it was trying to avoid fragmentation, which wasn't very
>   successfully and may not work at all if there are multiple devices.
>   The fragmentation is not a serious issue and given the chance of
>   hitting that race is extremely low, let's just ignore that [ Chris Meson ].

And in Patch 11 I can see that you've made an important fix to the
!folio_ref_freeze() block in __folio_migrate_mapping(): there had been a
swap_cluster_unlock(ci) which you've fixed to swap_cluster_unlock_irq(ci):
I was going to report that, with the WARNING and "BUG: sleeping function"s
it caused, but you're ahead of me.

Thanks also for fixing the shmem_replace_folio() locking and stats
update, which I'd noticed too (but never hit): looks good now.

Hugh

> - Patch 8 & 9: move some changes from Patch 9 to Patch 8 to avoid build
>   error, no code change. [ Baolin Wang ]
> - Patch 9: Fix locking section issue, should protect the shmem statistic
>   update with spin lock irq. Also fix an warn on condition.
> Link to V3:
> - https://lore.kernel.org/linux-mm/20250910160833.3464-1-ryncsn@gmail.com/