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Wed, 17 Dec 2025 03:44:53 -0800 (PST) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Wed, 17 Dec 2025 12:44:51 +0100 To: Baoquan He Cc: "Uladzislau Rezki (Sony)" , linux-mm@kvack.org, Andrew Morton , Vishal Moola , Ryan Roberts , Dev Jain , LKML Subject: Re: [PATCH 2/2] mm/vmalloc: Add attempt_larger_order_alloc parameter Message-ID: References: <20251216211921.1401147-1-urezki@gmail.com> <20251216211921.1401147-2-urezki@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Queue-Id: 3CEA4100003 X-Rspamd-Server: rspam04 X-Stat-Signature: rynyg3y1p7jawgto9keoiq3jk3e47k6e X-HE-Tag: 1765971895-178806 X-HE-Meta: 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 v2TMmdAK 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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 Wed, Dec 17, 2025 at 11:54:26AM +0800, Baoquan He wrote: > Hi Uladzislau, > > On 12/16/25 at 10:19pm, Uladzislau Rezki (Sony) wrote: > > Introduce a module parameter to enable or disable the large-order > > allocation path in vmalloc. High-order allocations are disabled by > > default so far, but users may explicitly enable them at runtime if > > desired. > > > > High-order pages allocated for vmalloc are immediately split into > > order-0 pages and later freed as order-0, which means they do not > > feed the per-CPU page caches. As a result, high-order attempts tend > > I don't get why order-0 do not feed the PCP caches. > "they" -> high-order pages. I should improve it. > > to bypass the PCP fastpath and fall back to the buddy allocator that > > can affect performance. > > > > However, when the PCP caches are empty, high-order allocations may > > show better performance characteristics especially for larger > > allocation requests. > > And when PCP is empty, high-order alloc show better performance. Could > you please help elaborate a little more about them? Thanks. > This is what i/we measured. See below example: # default order-3 Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 3718592 usec Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 3740495 usec Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 3737213 usec Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 3740765 usec # patch order-3 Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 3350391 usec Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 3374568 usec Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 3286374 usec Summary: fix_size_alloc_test passed: 1 failed: 0 xfailed: 0 repeat: 1 loops: 1000000 avg: 3261335 usec why higher-order wins, i think it is less cyclesto get one big chunk from the buddy instead of looping and pick one by one. -- Uladzislau Rezki