Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Thu, 11 Jun 2020 11:35:23 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Johannes Weiner <hannes@cmpxchg.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Alex Shi <alex.shi@linux.alibaba.com>,
        Joonsoo Kim <js1304@gmail.com>,
        Shakeel Butt <shakeelb@google.com>,
        Hugh Dickins <hughd@google.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Roman Gushchin <guro@fb.com>, linux-mm@kvack.org,
        cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-team@fb.com
Subject: Re: [PATCH 16/19] mm: memcontrol: charge swapin pages on
 instantiation
Message-ID: <20200611093523.GB20450@dhcp22.suse.cz>
References: <20200508183105.225460-1-hannes@cmpxchg.org>
 <20200508183105.225460-17-hannes@cmpxchg.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200508183105.225460-17-hannes@cmpxchg.org>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri 08-05-20 14:31:03, Johannes Weiner wrote:
[...]
> diff --git a/mm/memory.c b/mm/memory.c
> index 832ee914cbcf..93900b121b6e 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3125,9 +3125,20 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>  			page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma,
>  							vmf->address);
>  			if (page) {
> +				int err;
> +
>  				__SetPageLocked(page);
>  				__SetPageSwapBacked(page);
>  				set_page_private(page, entry.val);
> +
> +				/* Tell memcg to use swap ownership records */
> +				SetPageSwapCache(page);
> +				err = mem_cgroup_charge(page, vma->vm_mm,
> +							GFP_KERNEL, false);
> +				ClearPageSwapCache(page);
> +				if (err)
> +					goto out_page;

err would be a return value from try_charge and that can be -ENOMEM. Now
we almost never return ENOMEM for GFP_KERNEL single page charge. Except
for async OOM handling (oom_disabled v1). So this needs translation to
VM_FAULT_OOM.

I am not an expert on the swap code so I might have missed some subtle
issues but the rest of the patch seems reasonable to me.
-- 
Michal Hocko
SUSE Labs