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[95.203.3.14]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-596bfa48c5dsm4644152e87.77.2025.12.02.06.03.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 02 Dec 2025 06:03:12 -0800 (PST) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Tue, 2 Dec 2025 15:03:10 +0100 To: Barry Song <21cnbao@gmail.com> Cc: Uladzislau Rezki , akpm@linux-foundation.org, linux-mm@kvack.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org, Barry Song , Sumit Semwal , John Stultz , Maxime Ripard Subject: Re: [PATCH RFC] mm/vmap: map contiguous pages in batches whenever possible Message-ID: References: <20251122090343.81243-1-21cnbao@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 2686CC002C X-Stat-Signature: zmjshij5sf4skeo47udp7buxfj7ewhak X-Rspam-User: X-HE-Tag: 1764684195-589046 X-HE-Meta: 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 mPMf0sn2 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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 Tue, Dec 02, 2025 at 06:05:56AM +0800, Barry Song wrote: > On Mon, Dec 1, 2025 at 7:08 PM Uladzislau Rezki wrote: > > > > On Fri, Nov 28, 2025 at 04:43:54AM +0800, Barry Song wrote: > > > > > > > > > > + /* > > > > > + * Some users may allocate pages from high-order down to order 0. > > > > > + * We roughly check if the first page is a compound page. If so, > > > > > + * there is a chance to batch multiple pages together. > > > > > + */ > > > > > if (!IS_ENABLED(CONFIG_HAVE_ARCH_HUGE_VMALLOC) || > > > > > - page_shift == PAGE_SHIFT) > > > > > + (page_shift == PAGE_SHIFT && !PageCompound(pages[0]))) > > > > > > > > > Do we support __GFP_COMP as vmalloc/vmap flag? As i see from latest: > > > > > > This is not the case for vmalloc, but applies to dma-bufs that are allocated > > > using alloc_pages() with GFP_COMP. > > > > > > #define LOW_ORDER_GFP (GFP_HIGHUSER | __GFP_ZERO) > > > #define HIGH_ORDER_GFP (((GFP_HIGHUSER | __GFP_ZERO | __GFP_NOWARN \ > > > | __GFP_NORETRY) & ~__GFP_RECLAIM) \ > > > | __GFP_COMP) > > > > > > > > > > > /* > > > > * See __vmalloc_node_range() for a clear list of supported vmalloc flags. > > > > * This gfp lists all flags currently passed through vmalloc. Currently, > > > > * __GFP_ZERO is used by BPF and __GFP_NORETRY is used by percpu. Both drm > > > > * and BPF also use GFP_USER. Additionally, various users pass > > > > * GFP_KERNEL_ACCOUNT. Xfs uses __GFP_NOLOCKDEP. > > > > */ > > > > #define GFP_VMALLOC_SUPPORTED (GFP_KERNEL | GFP_ATOMIC | GFP_NOWAIT |\ > > > > __GFP_NOFAIL | __GFP_ZERO | __GFP_NORETRY |\ > > > > GFP_NOFS | GFP_NOIO | GFP_KERNEL_ACCOUNT |\ > > > > GFP_USER | __GFP_NOLOCKDEP) > > > > > > > > Could you please clarify when PageCompound(pages[0]) returns true? > > > > > > > > > > In this case, dma-buf attempts to allocate as many compound high-order pages > > > as possible, falling back to 0-order allocations if necessary. > > > > > OK, it is folio who uses it. > > > > > Then, dma_buf_vmap() is called by the GPU drivers: > > > > > > 1 404 drivers/accel/amdxdna/amdxdna_gem.c <> > > > dma_buf_vmap(abo->dma_buf, map); > > > 2 1568 drivers/dma-buf/dma-buf.c <> > > > ret = dma_buf_vmap(dmabuf, map); > > > 3 354 drivers/gpu/drm/drm_gem_shmem_helper.c > > > <> > > > ret = dma_buf_vmap(obj->import_attach->dmabuf, map); > > > 4 85 drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c > > > <> > > > ret = dma_buf_vmap(etnaviv_obj->base.import_attach->dmabuf, &map); > > > 5 433 drivers/gpu/drm/vmwgfx/vmwgfx_blit.c <> > > > ret = dma_buf_vmap(bo->tbo.base.dma_buf, map); > > > 6 88 drivers/gpu/drm/vmwgfx/vmwgfx_gem.c <> > > > ret = dma_buf_vmap(obj->import_attach->dmabuf, map); > > > > > Thank you for clarification. That would be good to reflect it in the > > commit message. Also, please note that: > > Sure. > > > > > > if (!IS_ENABLED(CONFIG_HAVE_ARCH_HUGE_VMALLOC) || > > > - page_shift == PAGE_SHIFT) > > > + (page_shift == PAGE_SHIFT && !PageCompound(pages[0]))) > > > > > we rely on page_shift == PAGE_SHIFT condition for the non-sleep vmalloc() > > allocations(GFP_ATOMIC, GFP_NOWAIT), so we go via vmap_small_pages_range_noflush() > > path. Your patch adds !PageCompound(pages[0]) also. It is not a problem > > since it is vmap() path but we need to comment that. > > Sure. Would the following work? > > /* > * For vmap(), users may allocate pages from high orders down > to order 0, > * while always using PAGE_SHIFT as the page_shift. > * We first check whether the initial page is a compound page. If so, > * there may be an opportunity to batch multiple pages together. > */ > if (!IS_ENABLED(CONFIG_HAVE_ARCH_HUGE_VMALLOC) || > (page_shift == PAGE_SHIFT && !PageCompound(pages[0]))) > return vmap_small_pages_range_noflush(addr, end, prot, pages); > Sounds good! Thank you. -- Uladzislau Rezki