linux-kernel - Re: [PATCHv4 0/4] zsmalloc: fine-grained fullness and new compaction algorithm

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Date:   Mon, 17 Apr 2023 20:24:21 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Yosry Ahmed <yosryahmed@...gle.com>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Yu Zhao <yuzhao@...gle.com>, Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv4 0/4] zsmalloc: fine-grained fullness and new compaction
 algorithm

On (23/04/17 04:16), Yosry Ahmed wrote:
> > That's a good question to which I don't have an answer. We can list_add()
> > the same zspage twice, unlocking the pool after first list_add() so that
> > another process (including another zs_compact()) can do something to that
> > zspage. The answer is somewhere between these lines, I guess.
> 
> But the first list_add() is (in this case) the correct add, so we
> expect other processes to be able to access the zspage after the first
> list_add() anyway, right?

Correct. Compaction also can unlock pool->lock and schedule() so that
another process can access the source zspage, when compaction gets
scheduled it can attempt putback/unlock the same zspage one more time
(the zspage may not even exist at this point, I assume).