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Tue, 16 Dec 2025 10:20:05 -0800 (PST) MIME-Version: 1.0 References: <20251206131955.780557-1-mjguzik@gmail.com> <20251206131955.780557-3-mjguzik@gmail.com> In-Reply-To: From: Mateusz Guzik Date: Tue, 16 Dec 2025 19:19:53 +0100 X-Gm-Features: AQt7F2qyzJWfM9FW-AbUmqEArqMlN00Wb8yGW298fF0nOnHl-1A2xmu_prHUnTk Message-ID: Subject: Re: [PATCH v3 2/2] pid: only take pidmap_lock once on alloc To: Tycho Andersen Cc: oleg@redhat.com, brauner@kernel.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, linux-mm@kvack.org, willy@infradead.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam02 X-Stat-Signature: cn3o8xea8dyn9exbr9635ig6xhxya4ho X-Rspam-User: X-Rspamd-Queue-Id: 706F81C000B X-HE-Tag: 1765909207-253043 X-HE-Meta: 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 af+xeeEC ZP7vGsPGNo+9hVgrszKzuPW630iOWAUqaXBRH0r/ke4RG8DfZQqxHxmwHKrPHD6A13nQMnmlNafRzifJpFwjiREg9uPz/qfoqs/TjF21IMNCMTA8pI+ab1gKmTyyYl00RIQdE7ClZSQ2UlQjjr6a+7ZyOh0teWHvZZO/yg9PYmayZuzYp78LjAVz9k4yhtJtH4rYt6lcSDVOJbB/3qm4YegfqurZEoQNVBPPSDk4aH69kj11lrXlnTFXz6S1rubWlEnxB0dmi/cl9dGEG1I9usSXJlBMdQLvyuRdI6bWoVid52oIOsXWk/C+GONvCPj7gWArCwyrSoLrF54teMjidCDJF+3VbRJK96CDTiRIRLQsKT9WrXhAZbt4wympowubBYsAzThrJL9COrSpVxovV0fkpYyTjUGZLFBgU2kNp1Abba6k= 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 Tue, Dec 16, 2025 at 6:09=E2=80=AFPM Tycho Andersen w= rote: > In a particularly pathological case I can get a substantial > improvement in kernel CPU time with this patch: > > Before: Time (mean =C2=B1 =CF=83): 53.007 s =C2=B1 0.148 s [Use= r: 430.891 s, System: 12406.459 s] > After : Time (mean =C2=B1 =CF=83): 45.624 s =C2=B1 0.394 s [Use= r: 435.021 s, System: 7692.072 s] > > across 10 different boots. Feel free to add > > Tested-by: Tycho Andersen (AMD) > thanks for testing > > + * (the routine unfortunately returns void, so we= have no idea if it got anywhere). > > Is it worth changing the return type? The underlying function looks > like it knows whether the allocation was actually successful... > willy says IDR is a stale api and the intent is to move consumers off of it. the loop is already a result of not changing the api, see v1 which add preload for more than one buffer. Whatever replacement should definitely indicate something like this if preload exists for its case.