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From: Shakeel Butt To: Usama Arif Cc: muchun.song@linux.dev, osalvador@suse.de, david@redhat.com, Andrew Morton , linux-mm@kvack.org, hannes@cmpxchg.org, riel@surriel.com, kas@kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH v2 2/2] mm/hugetlb: allow overcommitting gigantic hugepages Message-ID: <6bzfxls4dltmmogvjbr5q7wr2zf5grgcbla3mr4bah7kg6pdbu@qgx5lslkza57> References: <20251009172433.4158118-1-usamaarif642@gmail.com> <20251009172433.4158118-2-usamaarif642@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251009172433.4158118-2-usamaarif642@gmail.com> X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 28E24140004 X-Stat-Signature: jke98nqqxskyhi1tqbnyuekpetthgdwr X-HE-Tag: 1760056348-468677 X-HE-Meta: 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 68D53tZ5 2/FvnxKRknHd3Lmy+eFeXcPwCC7gbJgJg+Kt/nmxDfESEEX0NH4KVaxeKfn7DsM7hnFdPgY6EvL03qLeMLbMARvtH1JS9za3a+5TJPDWic9Af20Smxz1jIPQYLbF8GHGw9NsbUwRCVIZuoah3qT0/yb9pxsyl0DVz4Px8F4zUBsP29XYRu7nx4IfdnC7F34NoWkxvMd/nCI0hqblcgkdpBSwU0yRPpvTNLxW8gtYZZLbaWrl/jNiWnqHVfWblzLqKVosKzCQIEXhH23YctW8cT1z7Odd8zQ0Ag6SL 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 Thu, Oct 09, 2025 at 06:24:31PM +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. > > The restriction was added in 2011 [1], which was before there was support > for reserving 1G hugepages at runtime. > Remove this blanket restriction on gigantic hugepage overcommit. > This will bring the same benefits to gigantic pages as hugepages: > > - Memory is only taken out of regular use when actually needed > - Unused surplus pages can be returned to the system > - Better memory utilization, especially with CMA backing which can > significantly increase the changes of hugepage allocation > > Without this patch: > echo 3 > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_overcommit_hugepages > bash: echo: write error: Invalid argument > > With this patch: > echo 3 > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_overcommit_hugepages > ./mmap_hugetlb_test > Successfully allocated huge pages at address: 0x7f9d40000000 > > cat mmap_hugetlb_test.c > ... > unsigned long ALLOC_SIZE = 3 * (unsigned long) HUGE_PAGE_SIZE; > addr = mmap(NULL, > ALLOC_SIZE, // 3GB > PROT_READ | PROT_WRITE, > MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB | MAP_HUGE_1GB, > -1, > 0); > > if (addr == MAP_FAILED) { > fprintf(stderr, "mmap failed: %s\n", strerror(errno)); > return 1; > } > printf("Successfully allocated huge pages at address: %p\n", addr); > ... > > [1] https://git.zx2c4.com/linux-rng/commit/mm/hugetlb.c?id=adbe8726dc2a3805630d517270db17e3af86e526 > > Signed-off-by: Usama Arif Reviewed-by: Shakeel Butt