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Mon, 01 Dec 2025 03:08:25 -0800 (PST) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Mon, 1 Dec 2025 12:08:23 +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=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 44C9440019 X-Stat-Signature: 1m1ekxcg536h4uoeyrbma9kdpft4z858 X-HE-Tag: 1764587308-487834 X-HE-Meta: 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 AgFK9juD 3DZr0ewT/Rdfzzh9JyDXpyOUJcTvSXveYZALJFd1BP2mg/3e3lNM+6oTyeXUU+StQT270UKl4gaKXvpEgICSyHM8zfjR+27CwwX9tM4j/4/JI7366OS9uUMmPQa2KHXxHyXxcA152ZgIIGnL5LWTLhcfR/P7eGS8ZNWhK4LyiSqdjM9/BK6VMPoQQnCyJgxztk4trQA5qxEKvUgEAHole2n7318PKNH9Z/rZTG47zsBT9LoLbfN1vTWWSqkmSmyMDSe+4eE6oy7cTos+EPzoCiM8r0WYQFSadHeGJ0S0M1C9HbQ3v4vHBK4iF1C9SnFAn5Sh7KM+LTykvfryXJvAFviudPoXraPUvuA5pWBPY5pF58bpY22FNO+34SNPNqnBs1GhpZS8eJ6kk3dQvRCSNDB1nZgnNb8EDdFamvcMDZB6JMq5iq+9NunnqLNYcrS9QjdwHFkKIO5jakRKdRG8HiuUQhV0N+LCPF3UU 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, 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: > 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. -- Uladzislau Rezki