* Re: [PATCH v2] vduse: avoid using __GFP_NOFAIL [not found] <20240808054320.10017-1-jasowang@redhat.com> @ 2024-08-16 0:17 ` Barry Song 2024-08-16 2:03 ` Jason Wang 0 siblings, 1 reply; 2+ messages in thread From: Barry Song @ 2024-08-16 0:17 UTC (permalink / raw) To: Jason Wang Cc: mst, xuanzhuo, eperezma, maxime.coquelin, xieyongji, virtualization, linux-kernel, penguin-kernel, linux-mm, akpm On Thu, Aug 8, 2024 at 5:43 PM Jason Wang <jasowang@redhat.com> wrote: > > Barry said [1]: > > """ > mm doesn't support non-blockable __GFP_NOFAIL allocation. Because > __GFP_NOFAIL without direct reclamation may just result in a busy > loop within non-sleepable contexts. > > The current code will result in returning a NULL pointer but > not a busy-loop. > > static inline struct page * > __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > struct alloc_context *ac) > { > ... > /* > * Make sure that __GFP_NOFAIL request doesn't leak out and make sure > * we always retry > */ > 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; > } > > We have two choices to address the issue: > 1. busy-loop > 2. BUG_ON > > the below patch chose 2: > https://lore.kernel.org/linux-mm/20240731000155.109583-5-21cnbao@gmail.com/ > ""“ > > Unfortuantely, we do that under read 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 [2]: > > """ > 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 usersapce bounce pages. Then we don't need > to do allocation in the path which is not expected to be fail (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. > > [1] https://lore.kernel.org/all/CACGkMEtcOJAA96SF9B8m-nZ1X04-XZr+nq8ZQ2saLnUdfOGOLg@mail.gmail.com/T/#m3caef86a66ea6318ef94f9976ddb3a0ccfe6fcf8 > [2] https://lore.kernel.org/all/CACGkMEtcOJAA96SF9B8m-nZ1X04-XZr+nq8ZQ2saLnUdfOGOLg@mail.gmail.com/T/#m7ad10eaba48ade5abf2d572f24e185d9fb146480 > > Fixes: 6c77ed22880d ("vduse: Support using userspace pages as bounce buffer") > Reviewed-by: Xie Yongji <xieyongji@bytedance.com> > Tested-by: Xie Yongji <xieyongji@bytedance.com> > Signed-off-by: Jason Wang <jasowang@redhat.com> Hi Jason, Is this the final version to fix __GFP_NOFAIL issue, or will you have a new version? Do you prefer it to go through the mm tree or the drivers subsystem tree? If it's the former, I can send a new version that includes this one in my series[1]. [1] https://lore.kernel.org/linux-mm/20240731000155.109583-1-21cnbao@gmail.com/ > --- > Changes since V1: > - Tweak the commit log > - Assign map->user_bounce_page to NULL for safety > --- > 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; > memcpy_from_page(page_address(page), > - map->bounce_page, 0, PAGE_SIZE); > + map->user_bounce_page, 0, PAGE_SIZE); > } > - put_page(map->bounce_page); > - map->bounce_page = page; > + put_page(map->user_bounce_page); > + map->user_bounce_page = NULL; > } > domain->user_bounce_pages = false; > out: > diff --git a/drivers/vdpa/vdpa_user/iova_domain.h b/drivers/vdpa/vdpa_user/iova_domain.h > index f92f22a7267d..7f3f0928ec78 100644 > --- a/drivers/vdpa/vdpa_user/iova_domain.h > +++ b/drivers/vdpa/vdpa_user/iova_domain.h > @@ -21,6 +21,7 @@ > > struct vduse_bounce_map { > struct page *bounce_page; > + struct page *user_bounce_page; > u64 orig_phys; > }; > > -- > 2.31.1 > Thanks Barry ^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH v2] vduse: avoid using __GFP_NOFAIL 2024-08-16 0:17 ` [PATCH v2] vduse: avoid using __GFP_NOFAIL Barry Song @ 2024-08-16 2:03 ` Jason Wang 0 siblings, 0 replies; 2+ messages in thread From: Jason Wang @ 2024-08-16 2:03 UTC (permalink / raw) To: Barry Song Cc: mst, xuanzhuo, eperezma, maxime.coquelin, xieyongji, virtualization, linux-kernel, penguin-kernel, linux-mm, akpm On Fri, Aug 16, 2024 at 8:17 AM Barry Song <21cnbao@gmail.com> wrote: > > On Thu, Aug 8, 2024 at 5:43 PM Jason Wang <jasowang@redhat.com> wrote: > > > > Barry said [1]: > > > > """ > > mm doesn't support non-blockable __GFP_NOFAIL allocation. Because > > __GFP_NOFAIL without direct reclamation may just result in a busy > > loop within non-sleepable contexts. > > > > The current code will result in returning a NULL pointer but > > not a busy-loop. > > > > static inline struct page * > > __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > > struct alloc_context *ac) > > { > > ... > > /* > > * Make sure that __GFP_NOFAIL request doesn't leak out and make sure > > * we always retry > > */ > > 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; > > } > > > > We have two choices to address the issue: > > 1. busy-loop > > 2. BUG_ON > > > > the below patch chose 2: > > https://lore.kernel.org/linux-mm/20240731000155.109583-5-21cnbao@gmail.com/ > > ""“ > > > > Unfortuantely, we do that under read 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 [2]: > > > > """ > > 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 usersapce bounce pages. Then we don't need > > to do allocation in the path which is not expected to be fail (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. > > > > [1] https://lore.kernel.org/all/CACGkMEtcOJAA96SF9B8m-nZ1X04-XZr+nq8ZQ2saLnUdfOGOLg@mail.gmail.com/T/#m3caef86a66ea6318ef94f9976ddb3a0ccfe6fcf8 > > [2] https://lore.kernel.org/all/CACGkMEtcOJAA96SF9B8m-nZ1X04-XZr+nq8ZQ2saLnUdfOGOLg@mail.gmail.com/T/#m7ad10eaba48ade5abf2d572f24e185d9fb146480 > > > > Fixes: 6c77ed22880d ("vduse: Support using userspace pages as bounce buffer") > > Reviewed-by: Xie Yongji <xieyongji@bytedance.com> > > Tested-by: Xie Yongji <xieyongji@bytedance.com> > > Signed-off-by: Jason Wang <jasowang@redhat.com> > > Hi Jason, > > Is this the final version to fix __GFP_NOFAIL issue, or will you have a new > version? I think so. > Do you prefer it to go through the mm tree or the drivers subsystem tree? Either is fine. > If it's the former, I can send a new version that includes this one in my > series[1]. > > [1] https://lore.kernel.org/linux-mm/20240731000155.109583-1-21cnbao@gmail.com/ That's fine. Thanks > > > --- > > Changes since V1: > > - Tweak the commit log > > - Assign map->user_bounce_page to NULL for safety > > --- > > 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; > > memcpy_from_page(page_address(page), > > - map->bounce_page, 0, PAGE_SIZE); > > + map->user_bounce_page, 0, PAGE_SIZE); > > } > > - put_page(map->bounce_page); > > - map->bounce_page = page; > > + put_page(map->user_bounce_page); > > + map->user_bounce_page = NULL; > > } > > domain->user_bounce_pages = false; > > out: > > diff --git a/drivers/vdpa/vdpa_user/iova_domain.h b/drivers/vdpa/vdpa_user/iova_domain.h > > index f92f22a7267d..7f3f0928ec78 100644 > > --- a/drivers/vdpa/vdpa_user/iova_domain.h > > +++ b/drivers/vdpa/vdpa_user/iova_domain.h > > @@ -21,6 +21,7 @@ > > > > struct vduse_bounce_map { > > struct page *bounce_page; > > + struct page *user_bounce_page; > > u64 orig_phys; > > }; > > > > -- > > 2.31.1 > > > > Thanks > Barry > ^ permalink raw reply [flat|nested] 2+ messages in thread
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2024-08-16 0:17 ` [PATCH v2] vduse: avoid using __GFP_NOFAIL Barry Song
2024-08-16 2:03 ` Jason Wang
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