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: <20230109205336.3665937-1-surenb@google.com> <20230109205336.3665937-41-surenb@google.com>
 <CAG48ez1=-tY8nrsX+T=AJBmW05E8sAvZNj80Wev9sGwR9NZysQ@mail.gmail.com>
In-Reply-To: <CAG48ez1=-tY8nrsX+T=AJBmW05E8sAvZNj80Wev9sGwR9NZysQ@mail.gmail.com>
From:   Suren Baghdasaryan <surenb@google.com>
Date:   Tue, 17 Jan 2023 11:01:07 -0800
Message-ID: <CAJuCfpHSZouW44MqdZxpAB_NAdimdU2kcZ2sDo2mfNCf_nmL3w@mail.gmail.com>
Subject: Re: [PATCH 40/41] mm: separate vma->lock from vm_area_struct
To:     Jann Horn <jannh@google.com>
Cc:     akpm@linux-foundation.org, michel@lespinasse.org,
        jglisse@google.com, mhocko@suse.com, vbabka@suse.cz,
        hannes@cmpxchg.org, mgorman@techsingularity.net, dave@stgolabs.net,
        willy@infradead.org, liam.howlett@oracle.com, peterz@infradead.org,
        ldufour@linux.ibm.com, laurent.dufour@fr.ibm.com,
        paulmck@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,
        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 Tue, Jan 17, 2023 at 10:34 AM Jann Horn <jannh@google.com> wrote:
>
> On Mon, Jan 9, 2023 at 9:55 PM Suren Baghdasaryan <surenb@google.com> wrote:
> > vma->lock being part of the vm_area_struct causes performance regression
> > during page faults because during contention its count and owner fields
> > are constantly updated and having other parts of vm_area_struct used
> > during page fault handling next to them causes constant cache line
> > bouncing. Fix that by moving the lock outside of the vm_area_struct.
> > All attempts to keep vma->lock inside vm_area_struct in a separate
> > cache line still produce performance regression especially on NUMA
> > machines. Smallest regression was achieved when lock is placed in the
> > fourth cache line but that bloats vm_area_struct to 256 bytes.
>
> Just checking: When you tested putting the lock in different cache
> lines, did you force the slab allocator to actually store the
> vm_area_struct with cacheline alignment (by setting SLAB_HWCACHE_ALIGN
> on the slab or with a ____cacheline_aligned_in_smp on the struct
> definition)?

Yep, I tried all these combinations and still saw noticeable regression.