MIME-Version: 1.0
References: <20230125233554.153109-1-surenb@google.com> <20230125233554.153109-7-surenb@google.com>
 <20230126154740.j3a3lu4x557c56yi@techsingularity.net> <CAJuCfpHP6hQAWZr2exZEXOzLbMNU_c9qNNc7pa2NYAhYLe=EKQ@mail.gmail.com>
 <20230126173245.cf3jcfw5s2a77s5v@techsingularity.net>
In-Reply-To: <20230126173245.cf3jcfw5s2a77s5v@techsingularity.net>
From:   Suren Baghdasaryan <surenb@google.com>
Date:   Thu, 26 Jan 2023 09:34:35 -0800
Message-ID: <CAJuCfpGq6eqUWkptFn4FjRgPtYjCyc-CK1n3DADvEHnWd1t1Sw@mail.gmail.com>
Subject: Re: [PATCH v3 6/7] mm: introduce mod_vm_flags_nolock and use it in untrack_pfn
To:     Mel Gorman <mgorman@techsingularity.net>
Cc:     akpm@linux-foundation.org, michel@lespinasse.org,
        jglisse@google.com, mhocko@suse.com, vbabka@suse.cz,
        hannes@cmpxchg.org, dave@stgolabs.net, willy@infradead.org,
        liam.howlett@oracle.com, peterz@infradead.org,
        ldufour@linux.ibm.com, paulmck@kernel.org, mingo@redhat.com,
        will@kernel.org, luto@kernel.org, songliubraving@fb.com,
        peterx@redhat.com, david@redhat.com, dhowells@redhat.com,
        hughd@google.com, bigeasy@linutronix.de, kent.overstreet@linux.dev,
        punit.agrawal@bytedance.com, lstoakes@gmail.com,
        peterjung1337@gmail.com, rientjes@google.com,
        axelrasmussen@google.com, joelaf@google.com, minchan@google.com,
        jannh@google.com, shakeelb@google.com, tatashin@google.com,
        edumazet@google.com, gthelen@google.com, gurua@google.com,
        arjunroy@google.com, soheil@google.com, hughlynch@google.com,
        leewalsh@google.com, posk@google.com, linux-mm@kvack.org,
        linux-arm-kernel@lists.infradead.org,
        linuxppc-dev@lists.ozlabs.org, x86@kernel.org,
        linux-kernel@vger.kernel.org, kernel-team@android.com
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Thu, Jan 26, 2023 at 9:32 AM Mel Gorman <mgorman@techsingularity.net> wrote:
>
> On Thu, Jan 26, 2023 at 08:18:31AM -0800, Suren Baghdasaryan wrote:
> > On Thu, Jan 26, 2023 at 7:47 AM Mel Gorman <mgorman@techsingularity.net> wrote:
> > >
> > > On Wed, Jan 25, 2023 at 03:35:53PM -0800, Suren Baghdasaryan wrote:
> > > > In cases when VMA flags are modified after VMA was isolated and mmap_lock
> > > > was downgraded, flags modifications would result in an assertion because
> > > > mmap write lock is not held.
> > >
> > > Add note that it's also used during exit when the locking of the VMAs
> > > becomes irrelevant (mm users is 0, should be no VMA modifications taking
> > > place other than zap).
> >
> > Ack.
> >
> > >
> > > The typical naming pattern when a caller either knows it holds the necessary
> > > lock or knows it does not matter is __mod_vm_flags()
> >
> > Ok. It sounds less explicit but plenty of examples, so I'm fine with
> > such rename. Will apply in the next version.
> >
>
> It might be a personal thing. nolock to me is ambigious because it might
> mean "lock is already held", "no lock is necessary" or "no lock is acquired"
> where as *for me*, calling foo vs __foo *usually* means "direct callers of
> __foo take care of the locking, memory ordering, per-cpu pinning details etc"
> depending on the context. Of course, this convention is not universally true.
>
> > > > Pass a hint to untrack_pfn to conditionally use mod_vm_flags_nolock for
> > > > flags modification and to avoid assertion.
> > > >
> > > > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > >
> > > Patch itself looks ok. It strays close to being "conditional locking"
> > > though which might attract some complaints.
> >
> > The description seems to accurately describe what's done here but I'm
> > open to better suggestions.
>
> I don't have alternative suggestions but if someone else reads the patch and
> says "this is conditional locking", you can at least claim that someone
> else considered "conditional locking" and didn't think it was a major
> problem in this specific patch.

Perfect. Thanks!

>
> --
> Mel Gorman
> SUSE Labs