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AJvYcCWuEdTcUoxWe5Xxs8pJPeXTqBTc6ORa1XuD7crnR0tQup3HWX5BIZNqAMeGyPVbdFZycbcAr1ORwQ==@kvack.org X-Gm-Message-State: AOJu0YwNoVDsauFBha4Dgmc0Ye5P/vudveIaKkDkNwAfJApSxYDcPAlz aZM3VmLKOejcPynDk1WWrcYpWSpp/RW4FHuW8x/vbDoyOMvkUeGuEsc9X+swKyMd3xmoFHjTxZE g+M8d4xyYKQLb564F9jqR6rRc+p2xpmSxxuVhdA== X-Gm-Gg: ASbGncvH+vQmf5wv+hRnyH6NDukP9Eeza898q4XDHQAxGSTJChygZqCoqEcG5BoOiwP +7Vwp3n6eHhOIBicLJNPcF+qdArtOHKMqtz6ZYkOH5RQ1zJ8WaT9k7r44/3CGMurWdL5Z6Y5Phs ErVt8EaslEhTr8sb6PDPIy3g== X-Google-Smtp-Source: AGHT+IEggUeamsWLi4+mN8AQFPv64LyqLOXMAGAMy5pdzs9RcB8TH0r0+MP9HNhDEz3JJG9NIN3iJKr8Rd/vuBetlYc= X-Received: by 2002:a05:6512:4201:b0:545:2871:7cd5 with SMTP id 2adb3069b0e04-54fc67bf4f3mr629310e87.15.1746769773609; Thu, 08 May 2025 22:49:33 -0700 (PDT) MIME-Version: 1.0 References: <20250507-fork-fixes-v2-0-82ab1e42cde3@linaro.org> <20250507-fork-fixes-v2-5-82ab1e42cde3@linaro.org> In-Reply-To: From: Linus Walleij Date: Fri, 9 May 2025 07:49:22 +0200 X-Gm-Features: ATxdqUFBUL555ygI1eEkRc2_Hvcv3ybaKZiqsyecP6XSO25ZG5vZbbaU1ZyjNLI Message-ID: Subject: Re: [PATCH v2 5/5] fork: zero vmap stack using clear_page() instead of memset() To: Mateusz Guzik Cc: Andrew Morton , linux-mm@kvack.org, Pasha Tatashin Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 51D64C0002 X-Stat-Signature: roo5rb8uzehxwgegxts6ubwdkrhgmqn8 X-HE-Tag: 1746769775-172008 X-HE-Meta: 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 o0CKm5Fr iJ8gC1uEpVh/KGH3peOUbHm/LxIFoCiZMjMoc/65NaK+aSF/RmtBSHgMkBWPgeCaBR8VlEhpP38pnca0pgbqvxvssamORxOnDxeJHT09/2N4A6caUcdyHdQLGWRF3e3uLjb4D1vxE62nBn5l5PRm2Ma/XtKGEBmvdLdcjCJtqN7C014RbudA0Pv6MNTFtUFqDLZqUFghACDSshN3w2J93veKGZuJXjyGo/3AADnw2b3jALDjCGXROmr1ozsUTI4jb4hejAo/pT8JnuWGsDE/ZT+8yKz2A5z72UezHHFc1kTtwwP5cV+iVS/q2Ig== 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, May 7, 2025 at 6:51=E2=80=AFPM Mateusz Guzik wr= ote: > I don't know if the logic works here as far as the speed up goes -- you > are in fact *taking away* information what the caller is doing. > > In order to actually allow archs to optimize this you would need a > clearing func which grabs the page count. Aha so the information of how many pages get cleared is taken away from the call, if we assume that could be used by the arch. > There was a patchset to support multi-page clearing, but it only covers > x86-64: https://lore.kernel.org/all/20250414034607.762653-1-ankur.a.arora= @oracle.com/ (...) > tl;dr I think this patch should be dropped. if multi-page clearing shows > up for more archs then this is a thing to consider. Yeah I see the point, but I'm pretty sure I can make multi-page clearing work on aarch64 if that patch set goes in and then we can do something like this patch but for multipage. I'll put it on the back burner and resend. Thanks Mateusz, Linus Walleij