linux-kernel - Re: [PATCH] memcg: set page->private before calling swap

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Date:   Thu, 18 Mar 2021 09:55:14 +0100
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Hugh Dickins <hughd@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <guro@...com>, Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Minchan Kim <minchan@...nel.org>, cgroups@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] memcg: set page->private before calling swap_readpage

On Wed, Mar 17, 2021 at 06:59:59PM -0700, Shakeel Butt wrote:
> The function swap_readpage() (and other functions it call) extracts swap
> entry from page->private. However for SWP_SYNCHRONOUS_IO, the kernel
> skips the swapcache and thus we need to manually set the page->private
> with the swap entry before calling swap_readpage().
> 
> Signed-off-by: Shakeel Butt <shakeelb@...gle.com>
> Reported-by: Heiko Carstens <hca@...ux.ibm.com>
> ---
> 
> Andrew, please squash this into "memcg: charge before adding to
> swapcache on swapin" patch.
> 
>  mm/memory.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index aefd158ae1ea..b6f3410b5902 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3324,7 +3324,11 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>  					workingset_refault(page, shadow);
>  
>  				lru_cache_add(page);
> +
> +				/* To provide entry to swap_readpage() */
> +				set_page_private(page, entry.val);
>  				swap_readpage(page, true);
> +				set_page_private(page, 0);

Yes, this seems to fix it. Thanks a lot!

Tested-by: Heiko Carstens <hca@...ux.ibm.com>