linux-kernel - Re: [PATCH 16/19] mm: memcontrol: charge swapin pages on instantiation

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Date:   Thu, 11 Jun 2020 11:35:23 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Alex Shi <alex.shi@...ux.alibaba.com>,
        Joonsoo Kim <js1304@...il.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Hugh Dickins <hughd@...gle.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Roman Gushchin <guro@...com>, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH 16/19] mm: memcontrol: charge swapin pages on
 instantiation

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