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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-374cbbc8281sm1656354f8f.64.2024.09.02.00.33.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 02 Sep 2024 00:33:43 -0700 (PDT) Message-ID: <0804627b-49da-4ee0-a09a-19b87a7fdc3d@redhat.com> Date: Mon, 2 Sep 2024 09:33:42 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 1/3] vduse: avoid using __GFP_NOFAIL To: Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org, virtualization@lists.linux.dev Cc: 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, Jason Wang , Xie Yongji References: <20240830202823.21478-1-21cnbao@gmail.com> <20240830202823.21478-2-21cnbao@gmail.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: f4yeacah8p4rd5wpe77m9ni4cbkpxf9y X-Rspamd-Queue-Id: 9EC3040014 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1725262430-684786 X-HE-Meta: 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 st3rTD6n 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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 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? Maybe we should simply use memcpy_page(map->bounce_page, 0, map->user_bounce_page, 0, PAGE_SIZE) ? -- Cheers, David / dhildenb