linux-kernel - Re: [PATCH v4 14/15] mm, swap: implement dynamic allocation of swap table

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Message-ID: <CAGsJ_4zuLQeCDw8=O-bjxg2uaiq3wowa_5ZXyTGjeS7wGnrUgw@mail.gmail.com>
Date: Wed, 17 Sep 2025 06:51:31 +0800
From: Barry Song <21cnbao@...il.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>, 
	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 14/15] mm, swap: implement dynamic allocation of swap table

On Wed, Sep 17, 2025 at 12:02 AM Kairui Song <ryncsn@...il.com> wrote:
>
> From: Kairui Song <kasong@...cent.com>
>
> Now swap table is cluster based, which means free clusters can free its
> table since no one should modify it.
>
> There could be speculative readers, like swap cache look up, protect
> them by making them RCU protected. All swap table should be filled with
> null entries before free, so such readers will either see a NULL pointer
> or a null filled table being lazy freed.
>
> On allocation, allocate the table when a cluster is used by any order.
>
> This way, we can reduce the memory usage of large swap device
> significantly.
>
> This idea to dynamically release unused swap cluster data was initially
> suggested by Chris Li while proposing the cluster swap allocator and
> it suits the swap table idea very well.
>
> Co-developed-by: Chris Li <chrisl@...nel.org>
> Signed-off-by: Chris Li <chrisl@...nel.org>
> Signed-off-by: Kairui Song <kasong@...cent.com>

Reviewed-by: Barry Song <baohua@...nel.org>

Thanks
Barry