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Wed, 13 Nov 2024 07:25:37 -0800 (PST) MIME-Version: 1.0 References: <20241112194635.444146-1-surenb@google.com> <20241112194635.444146-5-surenb@google.com> <54b8d0b9-a1c7-4c1b-a588-2e5308a977fb@suse.cz> In-Reply-To: From: Suren Baghdasaryan Date: Wed, 13 Nov 2024 07:25:26 -0800 Message-ID: Subject: Re: [PATCH v2 4/5] mm: make vma cache SLAB_TYPESAFE_BY_RCU To: "Liam R. Howlett" , Matthew Wilcox , Vlastimil Babka , Suren Baghdasaryan , akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, mhocko@suse.com, hannes@cmpxchg.org, mjguzik@gmail.com, oliver.sang@intel.com, mgorman@techsingularity.net, david@redhat.com, peterx@redhat.com, oleg@redhat.com, dave@stgolabs.net, paulmck@kernel.org, brauner@kernel.org, dhowells@redhat.com, hdanton@sina.com, hughd@google.com, minchan@google.com, jannh@google.com, shakeel.butt@linux.dev, souravpanda@google.com, pasha.tatashin@soleen.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 3CF87120019 X-Stat-Signature: dzs84bkgk9dbgm5aiiqdjr1dx3766d7f X-Rspam-User: X-HE-Tag: 1731511482-784652 X-HE-Meta: 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 LWth2TEI ctAa283uuDNh1A2LD/Hq0zC1joZpOw24UIxRMXrp2O8VVvVPqYrPvsS8ek06RIx/TtGPuuDKxT1l1a/hZiMs8TBU5xiaIdveTvl57GF08yfKgpmIyGPgv9bzPa8ftvauU147vakCcZQWHo/YZfp8GeToSg7hnPHDqpkMAjEuOTG3WmErTAMgQHil6B65jtASj7Hx/t1rYe6A4+9gyiCE/te4FY5/5nbyNahVbKgFhVhoxMK7L2Za8dv9fm2hrWP3TGyITyOoYLELXkTnfweTdWnrLkmwcLJTKHiVlIZVOlU6kkTMh7Lt6265a7pLkA/7AI1fZ X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Nov 13, 2024 at 7:23=E2=80=AFAM 'Liam R. Howlett' via kernel-team wrote: > > * Matthew Wilcox [241113 08:57]: > > On Wed, Nov 13, 2024 at 07:38:02AM -0500, Liam R. Howlett wrote: > > > > Hi, I was wondering if we actually need the detached flag. Couldn't > > > > "detached" simply mean vma->vm_mm =3D=3D NULL and we save 4 bytes? = Do we ever > > > > need a vma that's detached but still has a mm pointer? I'd hope the= places > > > > that set detached to false have the mm pointer around so it's not i= nconvenient. > > > > > > I think the gate vmas ruin this plan. > > > > But the gate VMAs aren't to be found in the VMA tree. Used to be that > > was because the VMA tree was the injective RB tree and so VMAs could > > only be in one tree at a time. We could change that now! > > \o/ > > > > > Anyway, we could use (void *)1 instead of NULL to indicate a "detached" > > VMA if we need to distinguish between a detached VMA and a gate VMA. > > I was thinking a pointer to itself vma->vm_mm =3D vma, then a check for > this, instead of null like we do today. The motivation for having a separate detached flag was that vma->vm_mm is used when read/write locking the vma, so it has to stay valid even when vma gets detached. Maybe we can be more cautious in vma_start_read()/vma_start_write() about it but I don't recall if those were the only places that was an issue. > > Either way, we should make it a function so it's easier to reuse for > whatever we need in the future, wdyt? > > To unsubscribe from this group and stop receiving emails from it, send an= email to kernel-team+unsubscribe@android.com. >