Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20230501165450.15352-1-surenb@google.com> <20230501165450.15352-36-surenb@google.com>
 <ZFIPmnrSIdJ5yusM@dhcp22.suse.cz> <CAJuCfpGsvWupMbasqvwcMYsOOPxTQqi1ed5+=vyu-yoPQwwybg@mail.gmail.com>
 <ZFNoVfb+1W4NAh74@dhcp22.suse.cz>
In-Reply-To: <ZFNoVfb+1W4NAh74@dhcp22.suse.cz>
From:   Suren Baghdasaryan <surenb@google.com>
Date:   Thu, 4 May 2023 09:22:07 -0700
Message-ID: <CAJuCfpGUtw6cbjLsksGJKATZfTV0FEYRXwXT0pZV83XqQydBgg@mail.gmail.com>
Subject: Re: [PATCH 35/40] lib: implement context capture support for tagged allocations
To:     Michal Hocko <mhocko@suse.com>
Cc:     akpm@linux-foundation.org, kent.overstreet@linux.dev,
        vbabka@suse.cz, hannes@cmpxchg.org, roman.gushchin@linux.dev,
        mgorman@suse.de, dave@stgolabs.net, willy@infradead.org,
        liam.howlett@oracle.com, corbet@lwn.net, void@manifault.com,
        peterz@infradead.org, juri.lelli@redhat.com, ldufour@linux.ibm.com,
        catalin.marinas@arm.com, will@kernel.org, arnd@arndb.de,
        tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com,
        x86@kernel.org, peterx@redhat.com, david@redhat.com,
        axboe@kernel.dk, mcgrof@kernel.org, masahiroy@kernel.org,
        nathan@kernel.org, dennis@kernel.org, tj@kernel.org,
        muchun.song@linux.dev, rppt@kernel.org, paulmck@kernel.org,
        pasha.tatashin@soleen.com, yosryahmed@google.com,
        yuzhao@google.com, dhowells@redhat.com, hughd@google.com,
        andreyknvl@gmail.com, keescook@chromium.org,
        ndesaulniers@google.com, gregkh@linuxfoundation.org,
        ebiggers@google.com, ytcoode@gmail.com, vincent.guittot@linaro.org,
        dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
        bristot@redhat.com, vschneid@redhat.com, cl@linux.com,
        penberg@kernel.org, iamjoonsoo.kim@lge.com, 42.hyeyoo@gmail.com,
        glider@google.com, elver@google.com, dvyukov@google.com,
        shakeelb@google.com, songmuchun@bytedance.com, jbaron@akamai.com,
        rientjes@google.com, minchan@google.com, kaleshsingh@google.com,
        kernel-team@android.com, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, iommu@lists.linux.dev,
        linux-arch@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-mm@kvack.org, linux-modules@vger.kernel.org,
        kasan-dev@googlegroups.com, cgroups@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Thu, May 4, 2023 at 1:09=E2=80=AFAM Michal Hocko <mhocko@suse.com> wrote=
:
>
> On Wed 03-05-23 08:24:19, Suren Baghdasaryan wrote:
> > On Wed, May 3, 2023 at 12:39=E2=80=AFAM Michal Hocko <mhocko@suse.com> =
wrote:
> > >
> > > On Mon 01-05-23 09:54:45, Suren Baghdasaryan wrote:
> > > [...]
> > > > +struct codetag_ctx *alloc_tag_create_ctx(struct alloc_tag *tag, si=
ze_t size)
> > > > +{
> > > > +     struct alloc_call_ctx *ac_ctx;
> > > > +
> > > > +     /* TODO: use a dedicated kmem_cache */
> > > > +     ac_ctx =3D kmalloc(sizeof(struct alloc_call_ctx), GFP_KERNEL)=
;
> > >
> > > You cannot really use GFP_KERNEL here. This is post_alloc_hook path a=
nd
> > > that has its own gfp context.
> >
> > I missed that. Would it be appropriate to use the gfp_flags parameter
> > of post_alloc_hook() here?
>
> No. the original allocation could have been GFP_USER based and you do
> not want these allocations to pullute other zones potentially. You want
> GFP_KERNEL compatible subset of that mask.

Ack.

>
> But even then I really detest an additional allocation from this context
> for every single allocation request. There GFP_NOWAIT allocation for
> steckdepot but that is at least cached and generally not allocating.
> This will allocate for every single allocation.

A small correction here. alloc_tag_create_ctx() is used only for
allocations which we requested to capture the context. So, this last
sentence is true for allocations we specifically marked to capture the
context, not in general.

> There must be a better way.

Yeah, agree, it would be good to avoid allocations in this path. Any
specific ideas on how to improve this? Pooling/caching perhaps? I
think kmem_cache does some of that already but maybe something else?
Thanks,
Suren.

> --
> Michal Hocko
> SUSE Labs