linux-kernel - Re: [PATCH 1/2 v2] mm/zsmalloc.c: Migration can leave pages in ZS

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Date:   Tue, 20 Aug 2019 11:53:07 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Henry Burns <henryburns@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Minchan Kim <minchan@...nel.org>, Nitin Gupta <ngupta@...are.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Jonathan Adams <jwadams@...gle.com>,
        HenryBurns <henrywolfeburns@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2 v2] mm/zsmalloc.c: Migration can leave pages in
 ZS_EMPTY indefinitely

On (08/09/19 11:17), Henry Burns wrote:
> In zs_page_migrate() we call putback_zspage() after we have finished
> migrating all pages in this zspage. However, the return value is ignored.
> If a zs_free() races in between zs_page_isolate() and zs_page_migrate(),
> freeing the last object in the zspage, putback_zspage() will leave the page
> in ZS_EMPTY for potentially an unbounded amount of time.
> 
> To fix this, we need to do the same thing as zs_page_putback() does:
> schedule free_work to occur.  To avoid duplicated code, move the
> sequence to a new putback_zspage_deferred() function which both
> zs_page_migrate() and zs_page_putback() call.
> 
> Fixes: 48b4800a1c6a ("zsmalloc: page migration support")
> Signed-off-by: Henry Burns <henryburns@...gle.com>

Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>

+ Andrew

	-ss