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Peter Anvin" , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, linux-mm@kvack.org Subject: Re: [PATCH 5/5] mm: Do not map the shadow stack as THP Message-ID: <5570c06d-fbc1-42c9-9b27-26211e8b033c@sirena.org.uk> References: <20260224175800.2500729-1-catalin.marinas@arm.com> <20260224175800.2500729-6-catalin.marinas@arm.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="cXmct3hgznYcvsc+" Content-Disposition: inline In-Reply-To: <20260224175800.2500729-6-catalin.marinas@arm.com> X-Cookie: From concentrate. X-Rspamd-Queue-Id: DFA40140013 X-Stat-Signature: 3cgptmr6irba6dsb5xzmo9epfrj9aef3 X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1772024563-124679 X-HE-Meta: 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 yqs3E3wQ 2yktiaBw9lUjOtRFY9VhOufuxCbWSsN7kLIfa86eu3TzT4kdSBsZxXSFKlcKF5r4btnXPjSnQrna2ESQHH+TmXwR71GDppIzHKoQlulW0aahFPaBBNGkXmARcVGto/8IqJdZtXqs/VptP2Ki9pGfIv9lRlnp2C3MtjhPr4TPKZp2SSF4w1IVp9ZRNkDIqRwbdCbcgD5arBtF7aLHm+gktTzw4OqxcoVb0hKMze5BlFye89WAz184LzK3GI2WWAEeCZEiEjLJ9VH+Hb4/FbT7po0Qc/FOXahu/PDaHon5WCHJJDEAsIVE6c/mIdBW12IG2jlb6boa6GmV60hF+bxK6hnYGfjRXJGY5UwWxMnONc3C6ffY= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: --cXmct3hgznYcvsc+ Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Tue, Feb 24, 2026 at 05:57:57PM +0000, Catalin Marinas wrote: > The default shadow stack size allocated on first prctl() for the main > thread or subsequently on clone() is either half of RLIMIT_STACK or half > of a thread's stack size (for arm64). Both of these are likely to be > suitable for a THP allocation and the kernel is more aggressive in > creating such mappings. However, it does not make much sense to use a > huge page. It didn't make sense for the normal stacks either, see commit > c4608d1bf7c6 ("mm: mmap: map MAP_STACK to VM_NOHUGEPAGE"). Reviewed-by: Mark Brown The create THP and immediately splitting it pattern is very clear when checking the mm behaviour on new GCSs, this should help performance. --cXmct3hgznYcvsc+ Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAABCgAdFiEEreZoqmdXGLWf4p/qJNaLcl1Uh9AFAmme8usACgkQJNaLcl1U h9CDqwf6An6emWNltb5SR1AZIjifc5oF4Kkplg3VEBjz2qejH6O1DHtpUEPr90d1 /Np0MHYou2I8q7SWp4mdaNs1ovD2UT5Gr1SMFxZZBviJ0r9/Eob3BrpxVrC3QT9J qybG0P8RYytpWk5rc2TJllnyTlY7gcVhjDT7BqCec6wWQOmLFeLinB845irNXV16 fFjtAtMZw+1Gye+rZY1EeEKfdRZLlnkMneBaoKF0KSr4h5n8PvtcGAHHvzCral8n LS1poo8sjbOv0XtR6ZqTSEN0R7jQQ9w2QlZhaatEcZczugZRFs4jZDe7Q7HAZK1E yiaDOtnMo5LnFk3zQouQJMNjqU37lg== =SFPj -----END PGP SIGNATURE----- --cXmct3hgznYcvsc+--