memcg: remove a redundant check
Because of remove refcnt patch, it's very rare case to that mem_cgroup_charge_common() is called against a page which is accounted. mem_cgroup_charge_common() is called when. 1. a page is added into file cache. 2. an anon page is _newly_ mapped. A racy case is that a newly-swapped-in anonymous page is referred from prural threads in do_swap_page() at the same time. (a page is not Locked when mem_cgroup_charge() is called from do_swap_page.) Another case is shmem. It charges its page before calling add_to_page_cache(). Then, mem_cgroup_charge_cache() is called twice. This case is handled in mem_cgroup_cache_charge(). But this check may be too hacky... Signed-off-by : KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Balbir Singh <balbir@in.ibm.com> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Pavel Emelyanov <xemul@openvz.org> Cc: Li Zefan <lizf@cn.fujitsu.com> Cc: Hugh Dickins <hugh@veritas.com> Cc: YAMAMOTO Takashi <yamamoto@valinux.co.jp> Cc: Paul Menage <menage@google.com> Cc: David Rientjes <rientjes@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -536,28 +536,6 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
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if (mem_cgroup_subsys.disabled)
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return 0;
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/*
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* Should page_cgroup's go to their own slab?
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* One could optimize the performance of the charging routine
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* by saving a bit in the page_flags and using it as a lock
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* to see if the cgroup page already has a page_cgroup associated
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* with it
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*/
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retry:
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lock_page_cgroup(page);
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pc = page_get_page_cgroup(page);
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/*
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* The page_cgroup exists and
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* the page has already been accounted.
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*/
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if (unlikely(pc)) {
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VM_BUG_ON(pc->page != page);
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VM_BUG_ON(!pc->mem_cgroup);
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unlock_page_cgroup(page);
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goto done;
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}
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unlock_page_cgroup(page);
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pc = kmem_cache_alloc(page_cgroup_cache, gfp_mask);
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if (unlikely(pc == NULL))
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goto err;
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@ -618,15 +596,10 @@ retry:
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lock_page_cgroup(page);
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if (unlikely(page_get_page_cgroup(page))) {
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unlock_page_cgroup(page);
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/*
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* Another charge has been added to this page already.
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* We take lock_page_cgroup(page) again and read
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* page->cgroup, increment refcnt.... just retry is OK.
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*/
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res_counter_uncharge(&mem->res, PAGE_SIZE);
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css_put(&mem->css);
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kmem_cache_free(page_cgroup_cache, pc);
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goto retry;
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goto done;
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}
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page_assign_page_cgroup(page, pc);
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@ -665,8 +638,32 @@ int mem_cgroup_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask)
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int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
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gfp_t gfp_mask)
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{
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/*
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* Corner case handling. This is called from add_to_page_cache()
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* in usual. But some FS (shmem) precharges this page before calling it
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* and call add_to_page_cache() with GFP_NOWAIT.
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*
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* For GFP_NOWAIT case, the page may be pre-charged before calling
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* add_to_page_cache(). (See shmem.c) check it here and avoid to call
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* charge twice. (It works but has to pay a bit larger cost.)
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*/
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if (!(gfp_mask & __GFP_WAIT)) {
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struct page_cgroup *pc;
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lock_page_cgroup(page);
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pc = page_get_page_cgroup(page);
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if (pc) {
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VM_BUG_ON(pc->page != page);
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VM_BUG_ON(!pc->mem_cgroup);
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unlock_page_cgroup(page);
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return 0;
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}
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unlock_page_cgroup(page);
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}
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if (unlikely(!mm))
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mm = &init_mm;
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return mem_cgroup_charge_common(page, mm, gfp_mask,
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MEM_CGROUP_CHARGE_TYPE_CACHE, NULL);
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}
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