On Tue, Dec 02, 2025 at 06:05:56AM +0800, Barry Song wrote:
On Mon, Dec 1, 2025 at 7:08 PM Uladzislau Rezki urezki@gmail.com 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 <<amdxdna_gem_obj_vmap>> dma_buf_vmap(abo->dma_buf, map); 2 1568 drivers/dma-buf/dma-buf.c <<dma_buf_vmap_unlocked>> ret = dma_buf_vmap(dmabuf, map); 3 354 drivers/gpu/drm/drm_gem_shmem_helper.c <<drm_gem_shmem_vmap_locked>> ret = dma_buf_vmap(obj->import_attach->dmabuf, map); 4 85 drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c <<etnaviv_gem_prime_vmap_impl>> ret = dma_buf_vmap(etnaviv_obj->base.import_attach->dmabuf, &map); 5 433 drivers/gpu/drm/vmwgfx/vmwgfx_blit.c <<map_external>> ret = dma_buf_vmap(bo->tbo.base.dma_buf, map); 6 88 drivers/gpu/drm/vmwgfx/vmwgfx_gem.c <<vmw_gem_vmap>> 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 downto 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