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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1voNek-00000005OXd-32Ae; Fri, 06 Feb 2026 15:22:02 +0000 Date: Fri, 6 Feb 2026 15:22:02 +0000 From: Matthew Wilcox To: Dev Jain Cc: akpm@linux-foundation.org, david@kernel.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com, kirill@shutemov.name Subject: Re: [PATCH] mm: map maximum pages possible in finish_fault Message-ID: References: <20260206135648.38164-1-dev.jain@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260206135648.38164-1-dev.jain@arm.com> X-Rspamd-Queue-Id: 8C6BC80010 X-Stat-Signature: acwunrkpig8rp65sctdymcm6qm8naznw X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1770391327-988741 X-HE-Meta: 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 /KLm0iCg m/o1Z6Z5PT+XrGP5LK7+tyKfcRY6h1jHBETreUU51Ica7uFnsTAkEXnqehXLFTgnophILUthBrQKGJZlYM9v+5XrFtNri2pow4q9hNpH2A2cOw1Me+OWTS3TX14fDY2bM0OXMDO5G5AiHyHmB3rOPWm+rpCKSNGGmtVsKH0LhzUfLaAoRmlvH1r0eqbYyAS4VrP9tUCLKovhz2GPxNCpLzM7/c7Hx3F3K/Li/9UypP/Gz3bb33dq9VO79FjEhoUtJjEzbCjp1rngtpz0Bn/Z/ZuM1u/kr+/+27pDviR+iUGPQ1mE= 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 Fri, Feb 06, 2026 at 07:26:48PM +0530, Dev Jain wrote: > We test the patch with the following userspace program. A shmem VMA of > 2M is created, and faulted in, with sysfs setting > hugepages-2048k/shmem_enabled = always, so that the pagecache is populated > with a 2M folio. Then, a 64K VMA is created, and we fault on each page. > Then, we do MADV_DONTNEED to zap the pagetable, so that we can fault again > in the next iteration. We measure the accumulated time taken during > faulting the VMA. > > On arm64, > > without patch: > Total time taken by inner loop: 4701721766 ns > > with patch: > Total time taken by inner loop: 516043507 ns > > giving a 9x improvement. It's nice that you can construct a test-case that shows improvement, but is there any real workload that benefits from this?