Re: [PATCH v6] mm: retry page faults once under the per-VMA lock

[sashiko-bot@kernel.org]

> From: Hongru Zhang <zhanghongru@xiaomi.com>
> 
> The per-VMA lock fault path releases the per-VMA lock when the folio
> cannot be locked. It then waits for the folio to become lockable
> without holding the VMA lock and retries the page fault. However,
> the retry always takes the mmap_lock instead of the per-VMA lock.
> This can cause serious lock contention when a writer is holding the
> mmap_lock at the same time.
> 
> Add a single retry under the per-VMA lock in the architecture fault
> handler. This does not touch any page fault code in mm. The retry is
> very likely to succeed because the first page fault has already waited
> for the folio to become lockable. For example, this usually means that
> any required I/O has completed. This allows faults that can make
> progress on an immediate retry to stay on the per-VMA lock path,
> [ ... ]
> 
> [1] https://gist.github.com/zhr250/c36c2c54d9351df37e12fd072d4926ef
> [2] https://gist.github.com/zhr250/218ffe693f842346b56434483127422c
> 
> Signed-off-by: Hongru Zhang <zhanghongru@xiaomi.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260911025613.1220845-1-zhanghongru@xiaomi.com?part=1