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([2a02:6b6f:e750:1b00:1cfc:9209:4810:3ae5]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46fa9d6269asm10726435e9.15.2025.10.07.15.52.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 07 Oct 2025 15:52:47 -0700 (PDT) Message-ID: <09689e62-a8bd-4822-84ba-0f72f94fed52@gmail.com> Date: Tue, 7 Oct 2025 23:52:46 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/hugetlb: allow overcommitting gigantic hugepages Content-Language: en-GB To: Andrew Morton Cc: muchun.song@linux.dev, osalvador@suse.de, david@redhat.com, linux-mm@kvack.org, hannes@cmpxchg.org, riel@surriel.com, kas@kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, Shakeel Butt References: <20251006185607.3257340-1-usamaarif642@gmail.com> <20251007152429.4c28fb85205635703229b027@linux-foundation.org> From: Usama Arif In-Reply-To: <20251007152429.4c28fb85205635703229b027@linux-foundation.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: A77F9160008 X-Rspamd-Server: rspam02 X-Stat-Signature: qbrkn4jwctm91wsjgg366q7snhm5kipd X-HE-Tag: 1759877570-872623 X-HE-Meta: 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 NZ8zZJKm 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 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 07/10/2025 23:24, Andrew Morton wrote: > On Mon, 6 Oct 2025 19:56:07 +0100 Usama Arif wrote: > >> Currently, gigantic hugepages cannot use the overcommit mechanism >> (nr_overcommit_hugepages), forcing users to permanently reserve memory via >> nr_hugepages even when pages might not be actively used. >> > > Why did we do that? Just an oversight? I believe this restriction was added in 2011 [1], which was before there was support for reserving 1G hugepages at runtime. Once that was added, I think we forgot to remove this restriction. [1] https://git.zx2c4.com/linux-rng/commit/mm/hugetlb.c?id=adbe8726dc2a3805630d517270db17e3af86e526 > >> - if (hstate_is_gigantic(h)) >> + if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) > >> - if (hstate_is_gigantic(h)) >> + if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) > >> - if (write && hstate_is_gigantic(h)) >> + if (write && hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) > > Maybe a little helper for this? > > (Little helpers are nice sites for code comments!) Will add this in the next revision, Along with a paragraph about the history of why this restriction existed in the first place. Thanks for the review! Usama