linux-kernel - Re: [PATCH 2/4] memcg: unify force charging conditions

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Date:   Thu, 10 Feb 2022 14:25:01 -0800
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Roman Gushchin <guro@...com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...e.com>,
        Chris Down <chris@...isdown.name>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Cgroups <cgroups@...r.kernel.org>, Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] memcg: unify force charging conditions

On Thu, Feb 10, 2022 at 12:03 PM Roman Gushchin <guro@...com> wrote:
>
> On Thu, Feb 10, 2022 at 12:14:35AM -0800, Shakeel Butt wrote:
> > Currently the kernel force charges the allocations which have __GFP_HIGH
> > flag without triggering the memory reclaim. __GFP_HIGH indicates that
> > the caller is high priority and since commit 869712fd3de5 ("mm:
> > memcontrol: fix network errors from failing __GFP_ATOMIC charges") the
> > kernel let such allocations do force charging. Please note that
> > __GFP_ATOMIC has been replaced by __GFP_HIGH.
> >
> > __GFP_HIGH does not tell if the caller can block or can trigger reclaim.
> > There are separate checks to determine that. So, there is no need to
> > skip reclaim for __GFP_HIGH allocations. So, handle __GFP_HIGH together
> > with __GFP_NOFAIL which also does force charging.
>
> This sounds very reasonable. But shouldn't we check if __GFP_DIRECT_RECLAIM
> is set and bail out otherwise?
>

We already have a gfpflags_allow_blocking() check which checks for
__GFP_DIRECT_RECLAIM.