On Thu 23-06-11 19:01:57, KAMEZAWA Hiroyuki wrote: > From 7b0aa038f3a1c6a479a3ce6acb38c7d2740d7a75 Mon Sep 17 00:00:00 2001 > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > Date: Thu, 23 Jun 2011 18:50:32 +0900 > Subject: [PATCH] mm: preallocate page before lock_page() at filemap COW. > > Currently we are keeping faulted page locked throughout whole __do_fault > call (except for page_mkwrite code path) after calling file system's > fault code. If we do early COW, we allocate a new page which has to be > charged for a memcg (mem_cgroup_newpage_charge). > > This function, however, might block for unbounded amount of time if memcg > oom killer is disabled or fork-bomb is running because the only way out of > the OOM situation is either an external event or OOM-situation fix. > > In the end we are keeping the faulted page locked and blocking other > processes from faulting it in which is not good at all because we are > basically punishing potentially an unrelated process for OOM condition > in a different group (I have seen stuck system because of ld-2.11.1.so being > locked). > > We can do test easily. > > % cgcreate -g memory:A > % cgset -r memory.limit_in_bytes=64M A > % cgset -r memory.memsw.limit_in_bytes=64M A > % cd kernel_dir; cgexec -g memory:A make -j > > Then, the whole system will live-locked until you kill 'make -j' > by hands (or push reboot...) This is because some important > page in a shared library are locked. > > Considering again, the new page is not necessary to be allocated > with lock_page() held. So.... > > This patch moves "charge" and memory allocation for COW page > before lock_page(). Then, we can avoid scanning LRU with holding > a lock on a page. > > Then, above livelock disappears. > > Reported-by: Lutz Vieweg <lvml@xxxxxx> > Original-idea-by: Michal Hocko <mhocko@xxxxxxx> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> Sorry, forgot to send my Reviewed-by: Michal Hocko <mhocko@suse> I still have concerns about this way to handle the issue. See the follow up discussion in other thread (https://lkml.org/lkml/2011/6/23/135). Anyway I think that we do not have many other options to handle this. Either we unlock, charge, lock&restes or we preallocate, fault in Or am I missing some other ways how to do it? What do others think about these approaches? > > Changelog: > - change the logic from "do charge after unlock" to > "do charge before lock". > --- > mm/memory.c | 56 ++++++++++++++++++++++++++++++++++---------------------- > 1 files changed, 34 insertions(+), 22 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 87d9353..845378c 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -3127,14 +3127,34 @@ static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma, > pte_t *page_table; > spinlock_t *ptl; > struct page *page; > + struct page *cow_page; > pte_t entry; > int anon = 0; > - int charged = 0; > struct page *dirty_page = NULL; > struct vm_fault vmf; > int ret; > int page_mkwrite = 0; > > + /* > + * If we do COW later, allocate page befor taking lock_page() > + * on the file cache page. This will reduce lock holding time. > + */ > + if ((flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED)) { > + > + if (unlikely(anon_vma_prepare(vma))) > + return VM_FAULT_OOM; > + > + cow_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address); > + if (!cow_page) > + return VM_FAULT_OOM; > + > + if (mem_cgroup_newpage_charge(cow_page, mm, GFP_KERNEL)) { > + page_cache_release(cow_page); > + return VM_FAULT_OOM; > + } > + } else > + cow_page = NULL; > + > vmf.virtual_address = (void __user *)(address & PAGE_MASK); > vmf.pgoff = pgoff; > vmf.flags = flags; > @@ -3143,12 +3163,13 @@ static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma, > ret = vma->vm_ops->fault(vma, &vmf); > if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | > VM_FAULT_RETRY))) > - return ret; > + goto uncharge_out; > > if (unlikely(PageHWPoison(vmf.page))) { > if (ret & VM_FAULT_LOCKED) > unlock_page(vmf.page); > - return VM_FAULT_HWPOISON; > + ret = VM_FAULT_HWPOISON; > + goto uncharge_out; > } > > /* > @@ -3166,23 +3187,8 @@ static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma, > page = vmf.page; > if (flags & FAULT_FLAG_WRITE) { > if (!(vma->vm_flags & VM_SHARED)) { > + page = cow_page; > anon = 1; > - if (unlikely(anon_vma_prepare(vma))) { > - ret = VM_FAULT_OOM; > - goto out; > - } > - page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, > - vma, address); > - if (!page) { > - ret = VM_FAULT_OOM; > - goto out; > - } > - if (mem_cgroup_newpage_charge(page, mm, GFP_KERNEL)) { > - ret = VM_FAULT_OOM; > - page_cache_release(page); > - goto out; > - } > - charged = 1; > copy_user_highpage(page, vmf.page, address, vma); > __SetPageUptodate(page); > } else { > @@ -3251,8 +3257,8 @@ static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma, > /* no need to invalidate: a not-present page won't be cached */ > update_mmu_cache(vma, address, page_table); > } else { > - if (charged) > - mem_cgroup_uncharge_page(page); > + if (cow_page) > + mem_cgroup_uncharge_page(cow_page); > if (anon) > page_cache_release(page); > else > @@ -3261,7 +3267,6 @@ static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma, > > pte_unmap_unlock(page_table, ptl); > > -out: > if (dirty_page) { > struct address_space *mapping = page->mapping; > > @@ -3291,6 +3296,13 @@ out: > unwritable_page: > page_cache_release(page); > return ret; > +uncharge_out: > + /* fs's fault handler get error */ > + if (cow_page) { > + mem_cgroup_uncharge_page(cow_page); > + page_cache_release(cow_page); > + } > + return ret; > } > > static int do_linear_fault(struct mm_struct *mm, struct vm_area_struct *vma, > -- > 1.7.4.1 > > > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxx. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> -- Michal Hocko SUSE Labs SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>