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Message-ID: <20190805041440.GA178551@google.com>
Date: Mon, 5 Aug 2019 13:14:40 +0900
From: Minchan Kim <minchan@...nel.org>
To: Henry Burns <henryburns@...gle.com>
Cc: Nitin Gupta <ngupta@...are.org>,
Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
Shakeel Butt <shakeelb@...gle.com>,
Jonathan Adams <jwadams@...gle.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm/zsmalloc.c: Migration can leave pages in ZS_EMPTY
indefinitely
On Thu, Aug 01, 2019 at 06:53:31PM -0700, 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.
Nice catch.
>
> 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.
>
> Signed-off-by: Henry Burns <henryburns@...gle.com>
Cc: <stable@...r.kernel.org> [4.8+]
Acked-by: Minchan Kim <minchan@...nel.org>
Below a just trivial:
> ---
> mm/zsmalloc.c | 30 ++++++++++++++++++++----------
> 1 file changed, 20 insertions(+), 10 deletions(-)
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 1cda3fe0c2d9..efa660a87787 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -1901,6 +1901,22 @@ static void dec_zspage_isolation(struct zspage *zspage)
> zspage->isolated--;
> }
>
> +static void putback_zspage_deferred(struct zs_pool *pool,
> + struct size_class *class,
> + struct zspage *zspage)
> +{
> + enum fullness_group fg;
> +
> + fg = putback_zspage(class, zspage);
> + /*
> + * Due to page_lock, we cannot free zspage immediately
> + * so let's defer.
> + */
Could you move this comment function's description since it becomes
a function?
Thanks.
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