linux-kernel - Re: [PATCH v2 12/15] mm, swap: mark swap address space ro and add context debug check

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Message-ID: <55d54fd4-5360-457d-9da3-f5b14916c65b@redhat.com>
Date: Mon, 8 Sep 2025 15:10:46 +0200
From: David Hildenbrand <david@...hat.com>
To: Kairui Song <kasong@...cent.com>, linux-mm@...ck.org
Cc: 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>, Yosry Ahmed <yosryahmed@...gle.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Zi Yan <ziy@...dia.com>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 12/15] mm, swap: mark swap address space ro and add
 context debug check

On 05.09.25 21:13, Kairui Song wrote:
> From: Kairui Song <kasong@...cent.com>
> 
> Swap cache is now backed by swap table, and the address space is not
> holding any mutable data anymore. And swap cache is now protected by
> the swap cluster lock, instead of the XArray lock. All access to swap
> cache are wrapped by swap cache helpers. Locking is mostly handled
> internally by swap cache helpers, only a few __swap_cache_* helpers
> require the caller to lock the cluster by themselves.
> 
> Worth noting that, unlike XArray, the cluster lock is not IRQ safe.
> The swap cache was very different compared to filemap, and now it's
> completely separated from filemap. Nothing wants to mark or change
> anything or do a writeback callback in IRQ.
> 
> So explicitly document this and add a debug check to avoid further
> potential misuse. And mark the swap cache space as read-only to avoid
> any user wrongly mixing unexpected filemap helpers with swap cache.
> 
> Signed-off-by: Kairui Song <kasong@...cent.com>
> ---

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers

David / dhildenb