From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757000Ab2CWAyS (ORCPT ); Thu, 22 Mar 2012 20:54:18 -0400 Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:37116 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751785Ab2CWAyO (ORCPT ); Thu, 22 Mar 2012 20:54:14 -0400 X-SecurityPolicyCheck: OK by SHieldMailChecker v1.7.4 Message-ID: <4F6BC94C.80301@jp.fujitsu.com> Date: Fri, 23 Mar 2012 09:52:28 +0900 From: KAMEZAWA Hiroyuki User-Agent: Mozilla/5.0 (Windows NT 6.0; rv:10.0.2) Gecko/20120216 Thunderbird/10.0.2 MIME-Version: 1.0 To: Andrew Morton CC: "linux-mm@kvack.org" , Linux Kernel , "cgroups@vger.kernel.org" , Hugh Dickins , "n-horiguchi@ah.jp.nec.com" , Johannes Weiner , Michal Hocko , Glauber Costa Subject: Re: [PATCH] memcg: change behavior of moving charges at task move References: <4F69A4C4.4080602@jp.fujitsu.com> <20120322143610.e4df49c9.akpm@linux-foundation.org> <4F6BC166.80407@jp.fujitsu.com> <20120322173000.f078a43f.akpm@linux-foundation.org> In-Reply-To: <20120322173000.f078a43f.akpm@linux-foundation.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (2012/03/23 9:30), Andrew Morton wrote: > On Fri, 23 Mar 2012 09:18:46 +0900 KAMEZAWA Hiroyuki wrote: > >>>> +#ifdef CONFIG_SWAP >>>> + /* >>>> + * Avoid lookup_swap_cache() not to update statistics. >>>> + */ >>> >>> I don't understand this comment - what is it trying to tell us? >>> >> >> >> High Dickins advised me to use find_get_page() rather than lookup_swap_cache() >> because lookup_swap_cache() has some statistics with swap. > > ah. > > --- a/mm/memcontrol.c~memcg-change-behavior-of-moving-charges-at-task-move-fix > +++ a/mm/memcontrol.c > @@ -5137,7 +5137,8 @@ static struct page *mc_handle_swap_pte(s > return NULL; > #ifdef CONFIG_SWAP > /* > - * Avoid lookup_swap_cache() not to update statistics. > + * Use find_get_page() rather than lookup_swap_cache() because the > + * latter alters statistics. > */ > page = find_get_page(&swapper_space, ent.val); > #endif > >>>> + page = find_get_page(&swapper_space, ent.val); >>> >>> The code won't even compile if CONFIG_SWAP=n? >>> >> >> mm/built-in.o: In function `mc_handle_swap_pte': >> /home/kamezawa/Kernel/next/linux/mm/memcontrol.c:5172: undefined reference to `swapper_space' >> make: *** [.tmp_vmlinux1] Error 1 >> >> Ah...but I think this function (mc_handle_swap_pte) itself should be under CONFIG_SWAP. >> I'll post v2. > > Confused. The new reference to swapper_space is already inside #ifdef > CONFIG_SWAP. Sorry for confusion. Above log was I saw when I removed CONFIG_SWAP as a trial. How about this ? Maybe cleaner. == This patch changes memcg's behavior at task_move(). At task_move(), the kernel scans a task's page table and move the changes for mapped pages from source cgroup to target cgroup. There has been a bug at handling shared anonymous pages for a long time. Before patch: - The spec says 'shared anonymous pages are not moved.' - The implementation was 'shared anonymoys pages may be moved'. If page_mapcount <=2, shared anonymous pages's charge were moved. After patch: - The spec says 'all anonymous pages are moved'. - The implementation is 'all anonymous pages are moved'. Considering usage of memcg, this will not affect user's experience. 'shared anonymous' pages only exists between a tree of processes which don't do exec(). Moving one of process without exec() seems not sane. For example, libcgroup will not be affected by this change. (Anyway, no one noticed the implementation for a long time...) Below is a discussion log: - current spec/implementation are complex - Now, shared file caches are moved - It adds unclear check as page_mapcount(). To do correct check, we should check swap users, etc. - No one notice this implementation behavior. So, no one get benefit from the design. - In general, once task is moved to a cgroup for running, it will not be moved.... - Finally, we have control knob as memory.move_charge_at_immigrate. Here is a patch to allow moving shared pages, completely. This makes memcg simpler and fix current broken code. Changelog: - fixed comment around find_get_page() - changed CONFIG_SWAP handling - updated patch description Suggested-by: Hugh Dickins Signed-off-by: KAMEZAWA Hiroyuki --- Documentation/cgroups/memory.txt | 9 ++++----- include/linux/swap.h | 9 --------- mm/memcontrol.c | 22 ++++++++++++++-------- mm/swapfile.c | 31 ------------------------------- 4 files changed, 18 insertions(+), 53 deletions(-) diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt index 4c95c00..84d4f00 100644 --- a/Documentation/cgroups/memory.txt +++ b/Documentation/cgroups/memory.txt @@ -185,12 +185,14 @@ behind this approach is that a cgroup that aggressively uses a shared page will eventually get charged for it (once it is uncharged from the cgroup that brought it in -- this will happen on memory pressure). +But see section 8.2: when moving a task to another cgroup, its pages may +be recharged to the new cgroup, if move_charge_at_immigrate has been chosen. + Exception: If CONFIG_CGROUP_CGROUP_MEM_RES_CTLR_SWAP is not used. When you do swapoff and make swapped-out pages of shmem(tmpfs) to be backed into memory in force, charges for pages are accounted against the caller of swapoff rather than the users of shmem. - 2.4 Swap Extension (CONFIG_CGROUP_MEM_RES_CTLR_SWAP) Swap Extension allows you to record charge for swap. A swapped-in page is @@ -623,8 +625,7 @@ memory cgroup. bit | what type of charges would be moved ? -----+------------------------------------------------------------------------ 0 | A charge of an anonymous page(or swap of it) used by the target task. - | Those pages and swaps must be used only by the target task. You must - | enable Swap Extension(see 2.4) to enable move of swap charges. + | You must enable Swap Extension(see 2.4) to enable move of swap charges. -----+------------------------------------------------------------------------ 1 | A charge of file pages(normal file, tmpfs file(e.g. ipc shared memory) | and swaps of tmpfs file) mmapped by the target task. Unlike the case of @@ -637,8 +638,6 @@ memory cgroup. 8.3 TODO -- Implement madvise(2) to let users decide the vma to be moved or not to be - moved. - All of moving charge operations are done under cgroup_mutex. It's not good behavior to hold the mutex too long, so we may need some trick. diff --git a/include/linux/swap.h b/include/linux/swap.h index 6e66c03..70d2c74 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -387,7 +387,6 @@ static inline void deactivate_swap_token(struct mm_struct *mm, bool swap_token) #ifdef CONFIG_CGROUP_MEM_RES_CTLR extern void mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout); -extern int mem_cgroup_count_swap_user(swp_entry_t ent, struct page **pagep); #else static inline void mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout) @@ -532,14 +531,6 @@ mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent) { } -#ifdef CONFIG_CGROUP_MEM_RES_CTLR -static inline int -mem_cgroup_count_swap_user(swp_entry_t ent, struct page **pagep) -{ - return 0; -} -#endif - #endif /* CONFIG_SWAP */ #endif /* __KERNEL__*/ #endif /* _LINUX_SWAP_H */ diff --git a/mm/memcontrol.c b/mm/memcontrol.c index b2ee6df..ca8b3a1 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5147,7 +5147,7 @@ static struct page *mc_handle_present_pte(struct vm_area_struct *vma, return NULL; if (PageAnon(page)) { /* we don't move shared anon */ - if (!move_anon() || page_mapcount(page) > 2) + if (!move_anon()) return NULL; } else if (!move_file()) /* we ignore mapcount for file pages */ @@ -5158,26 +5158,32 @@ static struct page *mc_handle_present_pte(struct vm_area_struct *vma, return page; } +#ifdef CONFFIG_SWAP static struct page *mc_handle_swap_pte(struct vm_area_struct *vma, unsigned long addr, pte_t ptent, swp_entry_t *entry) { - int usage_count; struct page *page = NULL; swp_entry_t ent = pte_to_swp_entry(ptent); if (!move_anon() || non_swap_entry(ent)) return NULL; - usage_count = mem_cgroup_count_swap_user(ent, &page); - if (usage_count > 1) { /* we don't move shared anon */ - if (page) - put_page(page); - return NULL; - } + /* + * Because lookup_swap_cache() updates some statistics counter, + * we call find_get_page() with swapper_space directly. + */ + page = find_get_page(&swapper_space, ent.val); if (do_swap_account) entry->val = ent.val; return page; } +#else +static struct page *mc_handle_swap_pte(struct vm_area_struct *vma, + unsigned long addr, pte_t ptent, swp_entry_t *entry) +{ + return NULL; +} +#endif static struct page *mc_handle_file_pte(struct vm_area_struct *vma, unsigned long addr, pte_t ptent, swp_entry_t *entry) diff --git a/mm/swapfile.c b/mm/swapfile.c index dae42f3..fedeb6b 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -717,37 +717,6 @@ int free_swap_and_cache(swp_entry_t entry) return p != NULL; } -#ifdef CONFIG_CGROUP_MEM_RES_CTLR -/** - * mem_cgroup_count_swap_user - count the user of a swap entry - * @ent: the swap entry to be checked - * @pagep: the pointer for the swap cache page of the entry to be stored - * - * Returns the number of the user of the swap entry. The number is valid only - * for swaps of anonymous pages. - * If the entry is found on swap cache, the page is stored to pagep with - * refcount of it being incremented. - */ -int mem_cgroup_count_swap_user(swp_entry_t ent, struct page **pagep) -{ - struct page *page; - struct swap_info_struct *p; - int count = 0; - - page = find_get_page(&swapper_space, ent.val); - if (page) - count += page_mapcount(page); - p = swap_info_get(ent); - if (p) { - count += swap_count(p->swap_map[swp_offset(ent)]); - spin_unlock(&swap_lock); - } - - *pagep = page; - return count; -} -#endif - #ifdef CONFIG_HIBERNATION /* * Find the swap type that corresponds to given device (if any). -- 1.7.4.1 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx145.postini.com [74.125.245.145]) by kanga.kvack.org (Postfix) with SMTP id 2A4CF6B0044 for ; Thu, 22 Mar 2012 20:54:15 -0400 (EDT) Received: from m4.gw.fujitsu.co.jp (unknown [10.0.50.74]) by fgwmail6.fujitsu.co.jp (Postfix) with ESMTP id B8AB53EE0BB for ; Fri, 23 Mar 2012 09:54:13 +0900 (JST) Received: from smail (m4 [127.0.0.1]) by outgoing.m4.gw.fujitsu.co.jp (Postfix) with ESMTP id 9A00E45DE51 for ; Fri, 23 Mar 2012 09:54:13 +0900 (JST) Received: from s4.gw.fujitsu.co.jp (s4.gw.fujitsu.co.jp [10.0.50.94]) by m4.gw.fujitsu.co.jp (Postfix) with ESMTP id 77D1745DE4E for ; Fri, 23 Mar 2012 09:54:13 +0900 (JST) Received: from s4.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s4.gw.fujitsu.co.jp (Postfix) with ESMTP id 66DB21DB803B for ; Fri, 23 Mar 2012 09:54:13 +0900 (JST) Received: from ml13.s.css.fujitsu.com (ml13.s.css.fujitsu.com [10.240.81.133]) by s4.gw.fujitsu.co.jp (Postfix) with ESMTP id BFEB61DB8040 for ; Fri, 23 Mar 2012 09:54:12 +0900 (JST) Message-ID: <4F6BC94C.80301@jp.fujitsu.com> Date: Fri, 23 Mar 2012 09:52:28 +0900 From: KAMEZAWA Hiroyuki MIME-Version: 1.0 Subject: Re: [PATCH] memcg: change behavior of moving charges at task move References: <4F69A4C4.4080602@jp.fujitsu.com> <20120322143610.e4df49c9.akpm@linux-foundation.org> <4F6BC166.80407@jp.fujitsu.com> <20120322173000.f078a43f.akpm@linux-foundation.org> In-Reply-To: <20120322173000.f078a43f.akpm@linux-foundation.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: "linux-mm@kvack.org" , Linux Kernel , "cgroups@vger.kernel.org" , Hugh Dickins , "n-horiguchi@ah.jp.nec.com" , Johannes Weiner , Michal Hocko , Glauber Costa (2012/03/23 9:30), Andrew Morton wrote: > On Fri, 23 Mar 2012 09:18:46 +0900 KAMEZAWA Hiroyuki wrote: > >>>> +#ifdef CONFIG_SWAP >>>> + /* >>>> + * Avoid lookup_swap_cache() not to update statistics. >>>> + */ >>> >>> I don't understand this comment - what is it trying to tell us? >>> >> >> >> High Dickins advised me to use find_get_page() rather than lookup_swap_cache() >> because lookup_swap_cache() has some statistics with swap. > > ah. > > --- a/mm/memcontrol.c~memcg-change-behavior-of-moving-charges-at-task-move-fix > +++ a/mm/memcontrol.c > @@ -5137,7 +5137,8 @@ static struct page *mc_handle_swap_pte(s > return NULL; > #ifdef CONFIG_SWAP > /* > - * Avoid lookup_swap_cache() not to update statistics. > + * Use find_get_page() rather than lookup_swap_cache() because the > + * latter alters statistics. > */ > page = find_get_page(&swapper_space, ent.val); > #endif > >>>> + page = find_get_page(&swapper_space, ent.val); >>> >>> The code won't even compile if CONFIG_SWAP=n? >>> >> >> mm/built-in.o: In function `mc_handle_swap_pte': >> /home/kamezawa/Kernel/next/linux/mm/memcontrol.c:5172: undefined reference to `swapper_space' >> make: *** [.tmp_vmlinux1] Error 1 >> >> Ah...but I think this function (mc_handle_swap_pte) itself should be under CONFIG_SWAP. >> I'll post v2. > > Confused. The new reference to swapper_space is already inside #ifdef > CONFIG_SWAP. Sorry for confusion. Above log was I saw when I removed CONFIG_SWAP as a trial. How about this ? Maybe cleaner. == This patch changes memcg's behavior at task_move(). At task_move(), the kernel scans a task's page table and move the changes for mapped pages from source cgroup to target cgroup. There has been a bug at handling shared anonymous pages for a long time. Before patch: - The spec says 'shared anonymous pages are not moved.' - The implementation was 'shared anonymoys pages may be moved'. If page_mapcount <=2, shared anonymous pages's charge were moved. After patch: - The spec says 'all anonymous pages are moved'. - The implementation is 'all anonymous pages are moved'. Considering usage of memcg, this will not affect user's experience. 'shared anonymous' pages only exists between a tree of processes which don't do exec(). Moving one of process without exec() seems not sane. For example, libcgroup will not be affected by this change. (Anyway, no one noticed the implementation for a long time...) Below is a discussion log: - current spec/implementation are complex - Now, shared file caches are moved - It adds unclear check as page_mapcount(). To do correct check, we should check swap users, etc. - No one notice this implementation behavior. So, no one get benefit from the design. - In general, once task is moved to a cgroup for running, it will not be moved.... - Finally, we have control knob as memory.move_charge_at_immigrate. Here is a patch to allow moving shared pages, completely. This makes memcg simpler and fix current broken code. Changelog: - fixed comment around find_get_page() - changed CONFIG_SWAP handling - updated patch description Suggested-by: Hugh Dickins Signed-off-by: KAMEZAWA Hiroyuki --- Documentation/cgroups/memory.txt | 9 ++++----- include/linux/swap.h | 9 --------- mm/memcontrol.c | 22 ++++++++++++++-------- mm/swapfile.c | 31 ------------------------------- 4 files changed, 18 insertions(+), 53 deletions(-) diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt index 4c95c00..84d4f00 100644 --- a/Documentation/cgroups/memory.txt +++ b/Documentation/cgroups/memory.txt @@ -185,12 +185,14 @@ behind this approach is that a cgroup that aggressively uses a shared page will eventually get charged for it (once it is uncharged from the cgroup that brought it in -- this will happen on memory pressure). +But see section 8.2: when moving a task to another cgroup, its pages may +be recharged to the new cgroup, if move_charge_at_immigrate has been chosen. + Exception: If CONFIG_CGROUP_CGROUP_MEM_RES_CTLR_SWAP is not used. When you do swapoff and make swapped-out pages of shmem(tmpfs) to be backed into memory in force, charges for pages are accounted against the caller of swapoff rather than the users of shmem. - 2.4 Swap Extension (CONFIG_CGROUP_MEM_RES_CTLR_SWAP) Swap Extension allows you to record charge for swap. A swapped-in page is @@ -623,8 +625,7 @@ memory cgroup. bit | what type of charges would be moved ? -----+------------------------------------------------------------------------ 0 | A charge of an anonymous page(or swap of it) used by the target task. - | Those pages and swaps must be used only by the target task. You must - | enable Swap Extension(see 2.4) to enable move of swap charges. + | You must enable Swap Extension(see 2.4) to enable move of swap charges. -----+------------------------------------------------------------------------ 1 | A charge of file pages(normal file, tmpfs file(e.g. ipc shared memory) | and swaps of tmpfs file) mmapped by the target task. Unlike the case of @@ -637,8 +638,6 @@ memory cgroup. 8.3 TODO -- Implement madvise(2) to let users decide the vma to be moved or not to be - moved. - All of moving charge operations are done under cgroup_mutex. It's not good behavior to hold the mutex too long, so we may need some trick. diff --git a/include/linux/swap.h b/include/linux/swap.h index 6e66c03..70d2c74 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -387,7 +387,6 @@ static inline void deactivate_swap_token(struct mm_struct *mm, bool swap_token) #ifdef CONFIG_CGROUP_MEM_RES_CTLR extern void mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout); -extern int mem_cgroup_count_swap_user(swp_entry_t ent, struct page **pagep); #else static inline void mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout) @@ -532,14 +531,6 @@ mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent) { } -#ifdef CONFIG_CGROUP_MEM_RES_CTLR -static inline int -mem_cgroup_count_swap_user(swp_entry_t ent, struct page **pagep) -{ - return 0; -} -#endif - #endif /* CONFIG_SWAP */ #endif /* __KERNEL__*/ #endif /* _LINUX_SWAP_H */ diff --git a/mm/memcontrol.c b/mm/memcontrol.c index b2ee6df..ca8b3a1 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5147,7 +5147,7 @@ static struct page *mc_handle_present_pte(struct vm_area_struct *vma, return NULL; if (PageAnon(page)) { /* we don't move shared anon */ - if (!move_anon() || page_mapcount(page) > 2) + if (!move_anon()) return NULL; } else if (!move_file()) /* we ignore mapcount for file pages */ @@ -5158,26 +5158,32 @@ static struct page *mc_handle_present_pte(struct vm_area_struct *vma, return page; } +#ifdef CONFFIG_SWAP static struct page *mc_handle_swap_pte(struct vm_area_struct *vma, unsigned long addr, pte_t ptent, swp_entry_t *entry) { - int usage_count; struct page *page = NULL; swp_entry_t ent = pte_to_swp_entry(ptent); if (!move_anon() || non_swap_entry(ent)) return NULL; - usage_count = mem_cgroup_count_swap_user(ent, &page); - if (usage_count > 1) { /* we don't move shared anon */ - if (page) - put_page(page); - return NULL; - } + /* + * Because lookup_swap_cache() updates some statistics counter, + * we call find_get_page() with swapper_space directly. + */ + page = find_get_page(&swapper_space, ent.val); if (do_swap_account) entry->val = ent.val; return page; } +#else +static struct page *mc_handle_swap_pte(struct vm_area_struct *vma, + unsigned long addr, pte_t ptent, swp_entry_t *entry) +{ + return NULL; +} +#endif static struct page *mc_handle_file_pte(struct vm_area_struct *vma, unsigned long addr, pte_t ptent, swp_entry_t *entry) diff --git a/mm/swapfile.c b/mm/swapfile.c index dae42f3..fedeb6b 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -717,37 +717,6 @@ int free_swap_and_cache(swp_entry_t entry) return p != NULL; } -#ifdef CONFIG_CGROUP_MEM_RES_CTLR -/** - * mem_cgroup_count_swap_user - count the user of a swap entry - * @ent: the swap entry to be checked - * @pagep: the pointer for the swap cache page of the entry to be stored - * - * Returns the number of the user of the swap entry. The number is valid only - * for swaps of anonymous pages. - * If the entry is found on swap cache, the page is stored to pagep with - * refcount of it being incremented. - */ -int mem_cgroup_count_swap_user(swp_entry_t ent, struct page **pagep) -{ - struct page *page; - struct swap_info_struct *p; - int count = 0; - - page = find_get_page(&swapper_space, ent.val); - if (page) - count += page_mapcount(page); - p = swap_info_get(ent); - if (p) { - count += swap_count(p->swap_map[swp_offset(ent)]); - spin_unlock(&swap_lock); - } - - *pagep = page; - return count; -} -#endif - #ifdef CONFIG_HIBERNATION /* * Find the swap type that corresponds to given device (if any). -- 1.7.4.1 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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: email@kvack.org From mboxrd@z Thu Jan 1 00:00:00 1970 From: KAMEZAWA Hiroyuki Subject: Re: [PATCH] memcg: change behavior of moving charges at task move Date: Fri, 23 Mar 2012 09:52:28 +0900 Message-ID: <4F6BC94C.80301@jp.fujitsu.com> References: <4F69A4C4.4080602@jp.fujitsu.com> <20120322143610.e4df49c9.akpm@linux-foundation.org> <4F6BC166.80407@jp.fujitsu.com> <20120322173000.f078a43f.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20120322173000.f078a43f.akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Andrew Morton Cc: "linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org" , Linux Kernel , "cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Hugh Dickins , "n-horiguchi-PaJj6Psr51x8UrSeD/g0lQ@public.gmane.org" , Johannes Weiner , Michal Hocko , Glauber Costa (2012/03/23 9:30), Andrew Morton wrote: > On Fri, 23 Mar 2012 09:18:46 +0900 KAMEZAWA Hiroyuki wrote: > >>>> +#ifdef CONFIG_SWAP >>>> + /* >>>> + * Avoid lookup_swap_cache() not to update statistics. >>>> + */ >>> >>> I don't understand this comment - what is it trying to tell us? >>> >> >> >> High Dickins advised me to use find_get_page() rather than lookup_swap_cache() >> because lookup_swap_cache() has some statistics with swap. > > ah. > > --- a/mm/memcontrol.c~memcg-change-behavior-of-moving-charges-at-task-move-fix > +++ a/mm/memcontrol.c > @@ -5137,7 +5137,8 @@ static struct page *mc_handle_swap_pte(s > return NULL; > #ifdef CONFIG_SWAP > /* > - * Avoid lookup_swap_cache() not to update statistics. > + * Use find_get_page() rather than lookup_swap_cache() because the > + * latter alters statistics. > */ > page = find_get_page(&swapper_space, ent.val); > #endif > >>>> + page = find_get_page(&swapper_space, ent.val); >>> >>> The code won't even compile if CONFIG_SWAP=n? >>> >> >> mm/built-in.o: In function `mc_handle_swap_pte': >> /home/kamezawa/Kernel/next/linux/mm/memcontrol.c:5172: undefined reference to `swapper_space' >> make: *** [.tmp_vmlinux1] Error 1 >> >> Ah...but I think this function (mc_handle_swap_pte) itself should be under CONFIG_SWAP. >> I'll post v2. > > Confused. The new reference to swapper_space is already inside #ifdef > CONFIG_SWAP. Sorry for confusion. Above log was I saw when I removed CONFIG_SWAP as a trial. How about this ? Maybe cleaner. == This patch changes memcg's behavior at task_move(). At task_move(), the kernel scans a task's page table and move the changes for mapped pages from source cgroup to target cgroup. There has been a bug at handling shared anonymous pages for a long time. Before patch: - The spec says 'shared anonymous pages are not moved.' - The implementation was 'shared anonymoys pages may be moved'. If page_mapcount <=2, shared anonymous pages's charge were moved. After patch: - The spec says 'all anonymous pages are moved'. - The implementation is 'all anonymous pages are moved'. Considering usage of memcg, this will not affect user's experience. 'shared anonymous' pages only exists between a tree of processes which don't do exec(). Moving one of process without exec() seems not sane. For example, libcgroup will not be affected by this change. (Anyway, no one noticed the implementation for a long time...) Below is a discussion log: - current spec/implementation are complex - Now, shared file caches are moved - It adds unclear check as page_mapcount(). To do correct check, we should check swap users, etc. - No one notice this implementation behavior. So, no one get benefit from the design. - In general, once task is moved to a cgroup for running, it will not be moved.... - Finally, we have control knob as memory.move_charge_at_immigrate. Here is a patch to allow moving shared pages, completely. This makes memcg simpler and fix current broken code. Changelog: - fixed comment around find_get_page() - changed CONFIG_SWAP handling - updated patch description Suggested-by: Hugh Dickins Signed-off-by: KAMEZAWA Hiroyuki --- Documentation/cgroups/memory.txt | 9 ++++----- include/linux/swap.h | 9 --------- mm/memcontrol.c | 22 ++++++++++++++-------- mm/swapfile.c | 31 ------------------------------- 4 files changed, 18 insertions(+), 53 deletions(-) diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt index 4c95c00..84d4f00 100644 --- a/Documentation/cgroups/memory.txt +++ b/Documentation/cgroups/memory.txt @@ -185,12 +185,14 @@ behind this approach is that a cgroup that aggressively uses a shared page will eventually get charged for it (once it is uncharged from the cgroup that brought it in -- this will happen on memory pressure). +But see section 8.2: when moving a task to another cgroup, its pages may +be recharged to the new cgroup, if move_charge_at_immigrate has been chosen. + Exception: If CONFIG_CGROUP_CGROUP_MEM_RES_CTLR_SWAP is not used. When you do swapoff and make swapped-out pages of shmem(tmpfs) to be backed into memory in force, charges for pages are accounted against the caller of swapoff rather than the users of shmem. - 2.4 Swap Extension (CONFIG_CGROUP_MEM_RES_CTLR_SWAP) Swap Extension allows you to record charge for swap. A swapped-in page is @@ -623,8 +625,7 @@ memory cgroup. bit | what type of charges would be moved ? -----+------------------------------------------------------------------------ 0 | A charge of an anonymous page(or swap of it) used by the target task. - | Those pages and swaps must be used only by the target task. You must - | enable Swap Extension(see 2.4) to enable move of swap charges. + | You must enable Swap Extension(see 2.4) to enable move of swap charges. -----+------------------------------------------------------------------------ 1 | A charge of file pages(normal file, tmpfs file(e.g. ipc shared memory) | and swaps of tmpfs file) mmapped by the target task. Unlike the case of @@ -637,8 +638,6 @@ memory cgroup. 8.3 TODO -- Implement madvise(2) to let users decide the vma to be moved or not to be - moved. - All of moving charge operations are done under cgroup_mutex. It's not good behavior to hold the mutex too long, so we may need some trick. diff --git a/include/linux/swap.h b/include/linux/swap.h index 6e66c03..70d2c74 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -387,7 +387,6 @@ static inline void deactivate_swap_token(struct mm_struct *mm, bool swap_token) #ifdef CONFIG_CGROUP_MEM_RES_CTLR extern void mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout); -extern int mem_cgroup_count_swap_user(swp_entry_t ent, struct page **pagep); #else static inline void mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout) @@ -532,14 +531,6 @@ mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent) { } -#ifdef CONFIG_CGROUP_MEM_RES_CTLR -static inline int -mem_cgroup_count_swap_user(swp_entry_t ent, struct page **pagep) -{ - return 0; -} -#endif - #endif /* CONFIG_SWAP */ #endif /* __KERNEL__*/ #endif /* _LINUX_SWAP_H */ diff --git a/mm/memcontrol.c b/mm/memcontrol.c index b2ee6df..ca8b3a1 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5147,7 +5147,7 @@ static struct page *mc_handle_present_pte(struct vm_area_struct *vma, return NULL; if (PageAnon(page)) { /* we don't move shared anon */ - if (!move_anon() || page_mapcount(page) > 2) + if (!move_anon()) return NULL; } else if (!move_file()) /* we ignore mapcount for file pages */ @@ -5158,26 +5158,32 @@ static struct page *mc_handle_present_pte(struct vm_area_struct *vma, return page; } +#ifdef CONFFIG_SWAP static struct page *mc_handle_swap_pte(struct vm_area_struct *vma, unsigned long addr, pte_t ptent, swp_entry_t *entry) { - int usage_count; struct page *page = NULL; swp_entry_t ent = pte_to_swp_entry(ptent); if (!move_anon() || non_swap_entry(ent)) return NULL; - usage_count = mem_cgroup_count_swap_user(ent, &page); - if (usage_count > 1) { /* we don't move shared anon */ - if (page) - put_page(page); - return NULL; - } + /* + * Because lookup_swap_cache() updates some statistics counter, + * we call find_get_page() with swapper_space directly. + */ + page = find_get_page(&swapper_space, ent.val); if (do_swap_account) entry->val = ent.val; return page; } +#else +static struct page *mc_handle_swap_pte(struct vm_area_struct *vma, + unsigned long addr, pte_t ptent, swp_entry_t *entry) +{ + return NULL; +} +#endif static struct page *mc_handle_file_pte(struct vm_area_struct *vma, unsigned long addr, pte_t ptent, swp_entry_t *entry) diff --git a/mm/swapfile.c b/mm/swapfile.c index dae42f3..fedeb6b 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -717,37 +717,6 @@ int free_swap_and_cache(swp_entry_t entry) return p != NULL; } -#ifdef CONFIG_CGROUP_MEM_RES_CTLR -/** - * mem_cgroup_count_swap_user - count the user of a swap entry - * @ent: the swap entry to be checked - * @pagep: the pointer for the swap cache page of the entry to be stored - * - * Returns the number of the user of the swap entry. The number is valid only - * for swaps of anonymous pages. - * If the entry is found on swap cache, the page is stored to pagep with - * refcount of it being incremented. - */ -int mem_cgroup_count_swap_user(swp_entry_t ent, struct page **pagep) -{ - struct page *page; - struct swap_info_struct *p; - int count = 0; - - page = find_get_page(&swapper_space, ent.val); - if (page) - count += page_mapcount(page); - p = swap_info_get(ent); - if (p) { - count += swap_count(p->swap_map[swp_offset(ent)]); - spin_unlock(&swap_lock); - } - - *pagep = page; - return count; -} -#endif - #ifdef CONFIG_HIBERNATION /* * Find the swap type that corresponds to given device (if any). -- 1.7.4.1