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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-374b6a3d27fsm7704671f8f.59.2024.09.02.01.30.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 02 Sep 2024 01:30:36 -0700 (PDT) Message-ID: Date: Mon, 2 Sep 2024 10:30:35 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 1/3] vduse: avoid using __GFP_NOFAIL To: Jason Wang Cc: Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org, virtualization@lists.linux.dev, 42.hyeyoo@gmail.com, cl@linux.com, hailong.liu@oppo.com, hch@infradead.org, iamjoonsoo.kim@lge.com, mhocko@suse.com, penberg@kernel.org, rientjes@google.com, roman.gushchin@linux.dev, torvalds@linux-foundation.org, urezki@gmail.com, v-songbaohua@oppo.com, vbabka@suse.cz, laoar.shao@gmail.com, Xie Yongji References: <20240830202823.21478-1-21cnbao@gmail.com> <20240830202823.21478-2-21cnbao@gmail.com> <0804627b-49da-4ee0-a09a-19b87a7fdc3d@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Stat-Signature: 4c9oy15rwp3o88rb57bzgtst1axberbo X-Rspamd-Queue-Id: 546F22001F X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1725265843-434526 X-HE-Meta: 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 2jtkZyiD 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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 02.09.24 09:58, Jason Wang wrote: > On Mon, Sep 2, 2024 at 3:33 PM David Hildenbrand wrote: >> >> On 30.08.24 22:28, Barry Song wrote: >>> From: Jason Wang >>> >>> mm doesn't support non-blockable __GFP_NOFAIL allocation. Because >>> persisting in providing __GFP_NOFAIL services for non-block users >>> who cannot perform direct memory reclaim may only result in an >>> endless busy loop. >>> >>> Therefore, in such cases, the current mm-core may directly return >>> a NULL pointer: >>> >>> static inline struct page * >>> __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, >>> struct alloc_context *ac) >>> { >>> ... >>> if (gfp_mask & __GFP_NOFAIL) { >>> /* >>> * All existing users of the __GFP_NOFAIL are blockable, so warn >>> * of any new users that actually require GFP_NOWAIT >>> */ >>> if (WARN_ON_ONCE_GFP(!can_direct_reclaim, gfp_mask)) >>> goto fail; >>> ... >>> } >>> ... >>> fail: >>> warn_alloc(gfp_mask, ac->nodemask, >>> "page allocation failure: order:%u", order); >>> got_pg: >>> return page; >>> } >>> >>> Unfortuantely, vpda does that nofail allocation under non-sleepable >>> lock. A possible way to fix that is to move the pages allocation out >>> of the lock into the caller, but having to allocate a huge number of >>> pages and auxiliary page array seems to be problematic as well per >>> Tetsuon: " You should implement proper error handling instead of >>> using __GFP_NOFAIL if count can become large." >>> >>> So I choose another way, which does not release kernel bounce pages >>> when user tries to register userspace bounce pages. Then we can >>> avoid allocating in paths where failure is not expected.(e.g in >>> the release). We pay this for more memory usage as we don't release >>> kernel bounce pages but further optimizations could be done on top. >>> >>> Fixes: 6c77ed22880d ("vduse: Support using userspace pages as bounce buffer") >>> Reviewed-by: Xie Yongji >>> Tested-by: Xie Yongji >>> Signed-off-by: Jason Wang >>> [v-songbaohua@oppo.com: Refine the changelog] >>> Signed-off-by: Barry Song >>> --- >>> drivers/vdpa/vdpa_user/iova_domain.c | 19 +++++++++++-------- >>> drivers/vdpa/vdpa_user/iova_domain.h | 1 + >>> 2 files changed, 12 insertions(+), 8 deletions(-) >>> >>> diff --git a/drivers/vdpa/vdpa_user/iova_domain.c b/drivers/vdpa/vdpa_user/iova_domain.c >>> index 791d38d6284c..58116f89d8da 100644 >>> --- a/drivers/vdpa/vdpa_user/iova_domain.c >>> +++ b/drivers/vdpa/vdpa_user/iova_domain.c >>> @@ -162,6 +162,7 @@ static void vduse_domain_bounce(struct vduse_iova_domain *domain, >>> enum dma_data_direction dir) >>> { >>> struct vduse_bounce_map *map; >>> + struct page *page; >>> unsigned int offset; >>> void *addr; >>> size_t sz; >>> @@ -178,7 +179,10 @@ static void vduse_domain_bounce(struct vduse_iova_domain *domain, >>> map->orig_phys == INVALID_PHYS_ADDR)) >>> return; >>> >>> - addr = kmap_local_page(map->bounce_page); >>> + page = domain->user_bounce_pages ? >>> + map->user_bounce_page : map->bounce_page; >>> + >>> + addr = kmap_local_page(page); >>> do_bounce(map->orig_phys + offset, addr + offset, sz, dir); >>> kunmap_local(addr); >>> size -= sz; >>> @@ -270,9 +274,8 @@ int vduse_domain_add_user_bounce_pages(struct vduse_iova_domain *domain, >>> memcpy_to_page(pages[i], 0, >>> page_address(map->bounce_page), >>> PAGE_SIZE); >>> - __free_page(map->bounce_page); >>> } >>> - map->bounce_page = pages[i]; >>> + map->user_bounce_page = pages[i]; >>> get_page(pages[i]); >>> } >>> domain->user_bounce_pages = true; >>> @@ -297,17 +300,17 @@ void vduse_domain_remove_user_bounce_pages(struct vduse_iova_domain *domain) >>> struct page *page = NULL; >>> >>> map = &domain->bounce_maps[i]; >>> - if (WARN_ON(!map->bounce_page)) >>> + if (WARN_ON(!map->user_bounce_page)) >>> continue; >>> >>> /* Copy user page to kernel page if it's in use */ >>> if (map->orig_phys != INVALID_PHYS_ADDR) { >>> - page = alloc_page(GFP_ATOMIC | __GFP_NOFAIL); >>> + page = map->bounce_page; >> >> Why don't we need a kmap_local_page(map->bounce_page) here, but we might >> perform one / have performed one in vduse_domain_bounce? > > I think it's another bug that needs to be fixed. > > Yongji, do you want to fix this? Or maybe it works because "map->bounce_page" is now always a kernel page, and never one from user space that might reside in highmem. -- Cheers, David / dhildenb