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

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Message-ID: <YgWcjv/D7wy4dxXR@carbon.dhcp.thefacebook.com>
Date:   Thu, 10 Feb 2022 15:15:26 -0800
From:   Roman Gushchin <guro@...com>
To:     Shakeel Butt <shakeelb@...gle.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 02:25:01PM -0800, Shakeel Butt wrote:
> 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 __GFP_ATOMIC has been replaced by __GFP_HIGH.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.

Indeed. Please, feel free to add
Reviewed-by: Roman Gushchin <guro@...com> to the patch.

Thank you!