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Thu, 11 Dec 2025 07:39:47 -0800 (PST) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Thu, 11 Dec 2025 16:39:46 +0100 To: Ryan Roberts , "Vishal Moola (Oracle)" Cc: "Vishal Moola (Oracle)" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Uladzislau Rezki , Andrew Morton Subject: Re: [PATCH] mm/vmalloc: request large order pages from buddy allocator Message-ID: References: <20251021194455.33351-2-vishal.moola@gmail.com> <66919a28-bc81-49c9-b68f-dd7c73395a0d@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 9FB49C0014 X-Stat-Signature: haxkyhonk8ds78sc6ad8zu1i8bkn9afj X-Rspam-User: X-HE-Tag: 1765467590-276421 X-HE-Meta: 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 U/gPjKe7 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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 Thu, Dec 11, 2025 at 03:28:56PM +0000, Ryan Roberts wrote: > On 10/12/2025 22:28, Vishal Moola (Oracle) wrote: > > On Wed, Dec 10, 2025 at 01:21:22PM +0000, Ryan Roberts wrote: > >> Hi Vishal, > >> > >> > >> On 21/10/2025 20:44, Vishal Moola (Oracle) wrote: > >>> Sometimes, vm_area_alloc_pages() will want many pages from the buddy > >>> allocator. Rather than making requests to the buddy allocator for at > >>> most 100 pages at a time, we can eagerly request large order pages a > >>> smaller number of times. > >>> > >>> We still split the large order pages down to order-0 as the rest of the > >>> vmalloc code (and some callers) depend on it. We still defer to the bulk > >>> allocator and fallback path in case of order-0 pages or failure. > >>> > >>> Running 1000 iterations of allocations on a small 4GB system finds: > >>> > >>> 1000 2mb allocations: > >>> [Baseline] [This patch] > >>> real 46.310s real 0m34.582 > >>> user 0.001s user 0.006s > >>> sys 46.058s sys 0m34.365s > >>> > >>> 10000 200kb allocations: > >>> [Baseline] [This patch] > >>> real 56.104s real 0m43.696 > >>> user 0.001s user 0.003s > >>> sys 55.375s sys 0m42.995s > >> > >> I'm seeing some big vmalloc micro benchmark regressions on arm64, for which > >> bisect is pointing to this patch. > > > > Ulad had similar findings/concerns[1]. Tldr: The numbers you are seeing > > are expected for how the test module is currently written. > > Hmm... simplistically, I'd say that either the tests are bad, in which case they > should be deleted, or they are good, in which case we shouldn't ignore the > regressions. Having tests that we learn to ignore is the worst of both worlds. > Uh.. Tests are for measure vmalloc performance and stressing. They can not be just removed :) In some sense they are synthetic, from the other hand they allow to find problems and bottle-necks + measure perf. You have identified regression with it :) I think, the problem is in the + 14.05% 0.11% [kernel] [k] remove_vm_area + 11.85% 1.82% [kernel] [k] __alloc_frozen_pages_noprof + 10.91% 0.36% [kernel] [k] __get_vm_area_node + 10.60% 7.58% [kernel] [k] insert_vmap_area + 10.02% 4.67% [kernel] [k] get_page_from_freelist get_page_from_freelist() call. With a patch it adds 10% of cycles on top whereas without patch i do not see the symbol at all, i.e. pages are obtained really fast from the pcp list, not from the body. The question is, why high-order pages are not end-up in the pcp-cache? I think it is due to the fact, that we split such pages and freeing them as order-0 one. Any thoughts? -- Uladzislau Rezki