Re: [PATCH mmotm 2.5/4] memcg: disable irq at page cgroup lock(Re: [PATCH -mmotm 3/4] memcg: dirty pages accounting and limitinginfrastructure)
From: Andrea Righi
Date: Tue Mar 09 2010 - 04:07:17 EST
On Tue, Mar 09, 2010 at 10:29:28AM +0900, Daisuke Nishimura wrote:
> On Tue, 9 Mar 2010 09:19:14 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> > On Tue, 9 Mar 2010 01:12:52 +0100
> > Andrea Righi <arighi@xxxxxxxxxxx> wrote:
> >
> > > On Mon, Mar 08, 2010 at 05:31:00PM +0900, KAMEZAWA Hiroyuki wrote:
> > > > On Mon, 8 Mar 2010 17:07:11 +0900
> > > > Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx> wrote:
> > > >
> > > > > On Mon, 8 Mar 2010 11:37:11 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> > > > > > On Mon, 8 Mar 2010 11:17:24 +0900
> > > > > > Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx> wrote:
> > > > > >
> > > > > > > > But IIRC, clear_writeback is done under treelock.... No ?
> > > > > > > >
> > > > > > > The place where NR_WRITEBACK is updated is out of tree_lock.
> > > > > > >
> > > > > > > 1311 int test_clear_page_writeback(struct page *page)
> > > > > > > 1312 {
> > > > > > > 1313 struct address_space *mapping = page_mapping(page);
> > > > > > > 1314 int ret;
> > > > > > > 1315
> > > > > > > 1316 if (mapping) {
> > > > > > > 1317 struct backing_dev_info *bdi = mapping->backing_dev_info;
> > > > > > > 1318 unsigned long flags;
> > > > > > > 1319
> > > > > > > 1320 spin_lock_irqsave(&mapping->tree_lock, flags);
> > > > > > > 1321 ret = TestClearPageWriteback(page);
> > > > > > > 1322 if (ret) {
> > > > > > > 1323 radix_tree_tag_clear(&mapping->page_tree,
> > > > > > > 1324 page_index(page),
> > > > > > > 1325 PAGECACHE_TAG_WRITEBACK);
> > > > > > > 1326 if (bdi_cap_account_writeback(bdi)) {
> > > > > > > 1327 __dec_bdi_stat(bdi, BDI_WRITEBACK);
> > > > > > > 1328 __bdi_writeout_inc(bdi);
> > > > > > > 1329 }
> > > > > > > 1330 }
> > > > > > > 1331 spin_unlock_irqrestore(&mapping->tree_lock, flags);
> > > > > > > 1332 } else {
> > > > > > > 1333 ret = TestClearPageWriteback(page);
> > > > > > > 1334 }
> > > > > > > 1335 if (ret)
> > > > > > > 1336 dec_zone_page_state(page, NR_WRITEBACK);
> > > > > > > 1337 return ret;
> > > > > > > 1338 }
> > > > > >
> > > > > > We can move this up to under tree_lock. Considering memcg, all our target has "mapping".
> > > > > >
> > > > > > If we newly account bounce-buffers (for NILFS, FUSE, etc..), which has no ->mapping,
> > > > > > we need much more complex new charge/uncharge theory.
> > > > > >
> > > > > > But yes, adding new lock scheme seems complicated. (Sorry Andrea.)
> > > > > > My concerns is performance. We may need somehing new re-implementation of
> > > > > > locks/migrate/charge/uncharge.
> > > > > >
> > > > > I agree. Performance is my concern too.
> > > > >
> > > > > I made a patch below and measured the time(average of 10 times) of kernel build
> > > > > on tmpfs(make -j8 on 8 CPU machine with 2.6.33 defconfig).
> > > > >
> > > > > <before>
> > > > > - root cgroup: 190.47 sec
> > > > > - child cgroup: 192.81 sec
> > > > >
> > > > > <after>
> > > > > - root cgroup: 191.06 sec
> > > > > - child cgroup: 193.06 sec
> > > > >
> > > > > Hmm... about 0.3% slower for root, 0.1% slower for child.
> > > > >
> > > >
> > > > Hmm...accepatable ? (sounds it's in error-range)
> > > >
> > > > BTW, why local_irq_disable() ?
> > > > local_irq_save()/restore() isn't better ?
> > >
> > > Probably there's not the overhead of saving flags?
> > maybe.
> >
> > > Anyway, it would make the code much more readable...
> > >
> > ok.
> >
> > please go ahead in this direction. Nishimura-san, would you post an
> > independent patch ? If no, Andrea-san, please.
> >
> This is the updated version.
>
> Andrea-san, can you merge this into your patch set ?
OK, I'll merge, do some tests and post a new version.
Thanks!
-Andrea
>
> ===
> From: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
>
> In current implementation, we don't have to disable irq at lock_page_cgroup()
> because the lock is never acquired in interrupt context.
> But we are going to call it in later patch in an interrupt context or with
> irq disabled, so this patch disables irq at lock_page_cgroup() and enables it
> at unlock_page_cgroup().
>
> Signed-off-by: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
> ---
> include/linux/page_cgroup.h | 16 ++++++++++++++--
> mm/memcontrol.c | 43 +++++++++++++++++++++++++------------------
> 2 files changed, 39 insertions(+), 20 deletions(-)
>
> diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
> index 30b0813..0d2f92c 100644
> --- a/include/linux/page_cgroup.h
> +++ b/include/linux/page_cgroup.h
> @@ -83,16 +83,28 @@ static inline enum zone_type page_cgroup_zid(struct page_cgroup *pc)
> return page_zonenum(pc->page);
> }
>
> -static inline void lock_page_cgroup(struct page_cgroup *pc)
> +static inline void __lock_page_cgroup(struct page_cgroup *pc)
> {
> bit_spin_lock(PCG_LOCK, &pc->flags);
> }
>
> -static inline void unlock_page_cgroup(struct page_cgroup *pc)
> +static inline void __unlock_page_cgroup(struct page_cgroup *pc)
> {
> bit_spin_unlock(PCG_LOCK, &pc->flags);
> }
>
> +#define lock_page_cgroup(pc, flags) \
> + do { \
> + local_irq_save(flags); \
> + __lock_page_cgroup(pc); \
> + } while (0)
> +
> +#define unlock_page_cgroup(pc, flags) \
> + do { \
> + __unlock_page_cgroup(pc); \
> + local_irq_restore(flags); \
> + } while (0)
> +
> #else /* CONFIG_CGROUP_MEM_RES_CTLR */
> struct page_cgroup;
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 7fab84e..a9fd736 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1352,12 +1352,13 @@ void mem_cgroup_update_file_mapped(struct page *page, int val)
> {
> struct mem_cgroup *mem;
> struct page_cgroup *pc;
> + unsigned long flags;
>
> pc = lookup_page_cgroup(page);
> if (unlikely(!pc))
> return;
>
> - lock_page_cgroup(pc);
> + lock_page_cgroup(pc, flags);
> mem = pc->mem_cgroup;
> if (!mem)
> goto done;
> @@ -1371,7 +1372,7 @@ void mem_cgroup_update_file_mapped(struct page *page, int val)
> __this_cpu_add(mem->stat->count[MEM_CGROUP_STAT_FILE_MAPPED], val);
>
> done:
> - unlock_page_cgroup(pc);
> + unlock_page_cgroup(pc, flags);
> }
>
> /*
> @@ -1705,11 +1706,12 @@ struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
> struct page_cgroup *pc;
> unsigned short id;
> swp_entry_t ent;
> + unsigned long flags;
>
> VM_BUG_ON(!PageLocked(page));
>
> pc = lookup_page_cgroup(page);
> - lock_page_cgroup(pc);
> + lock_page_cgroup(pc, flags);
> if (PageCgroupUsed(pc)) {
> mem = pc->mem_cgroup;
> if (mem && !css_tryget(&mem->css))
> @@ -1723,7 +1725,7 @@ struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
> mem = NULL;
> rcu_read_unlock();
> }
> - unlock_page_cgroup(pc);
> + unlock_page_cgroup(pc, flags);
> return mem;
> }
>
> @@ -1736,13 +1738,15 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
> struct page_cgroup *pc,
> enum charge_type ctype)
> {
> + unsigned long flags;
> +
> /* try_charge() can return NULL to *memcg, taking care of it. */
> if (!mem)
> return;
>
> - lock_page_cgroup(pc);
> + lock_page_cgroup(pc, flags);
> if (unlikely(PageCgroupUsed(pc))) {
> - unlock_page_cgroup(pc);
> + unlock_page_cgroup(pc, flags);
> mem_cgroup_cancel_charge(mem);
> return;
> }
> @@ -1772,7 +1776,7 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
>
> mem_cgroup_charge_statistics(mem, pc, true);
>
> - unlock_page_cgroup(pc);
> + unlock_page_cgroup(pc, flags);
> /*
> * "charge_statistics" updated event counter. Then, check it.
> * Insert ancestor (and ancestor's ancestors), to softlimit RB-tree.
> @@ -1842,12 +1846,13 @@ static int mem_cgroup_move_account(struct page_cgroup *pc,
> struct mem_cgroup *from, struct mem_cgroup *to, bool uncharge)
> {
> int ret = -EINVAL;
> - lock_page_cgroup(pc);
> + unsigned long flags;
> + lock_page_cgroup(pc, flags);
> if (PageCgroupUsed(pc) && pc->mem_cgroup == from) {
> __mem_cgroup_move_account(pc, from, to, uncharge);
> ret = 0;
> }
> - unlock_page_cgroup(pc);
> + unlock_page_cgroup(pc, flags);
> /*
> * check events
> */
> @@ -1974,17 +1979,17 @@ int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
> */
> if (!(gfp_mask & __GFP_WAIT)) {
> struct page_cgroup *pc;
> -
> + unsigned long flags;
>
> pc = lookup_page_cgroup(page);
> if (!pc)
> return 0;
> - lock_page_cgroup(pc);
> + lock_page_cgroup(pc, flags);
> if (PageCgroupUsed(pc)) {
> - unlock_page_cgroup(pc);
> + unlock_page_cgroup(pc, flags);
> return 0;
> }
> - unlock_page_cgroup(pc);
> + unlock_page_cgroup(pc, flags);
> }
>
> if (unlikely(!mm && !mem))
> @@ -2166,6 +2171,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
> struct page_cgroup *pc;
> struct mem_cgroup *mem = NULL;
> struct mem_cgroup_per_zone *mz;
> + unsigned long flags;
>
> if (mem_cgroup_disabled())
> return NULL;
> @@ -2180,7 +2186,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
> if (unlikely(!pc || !PageCgroupUsed(pc)))
> return NULL;
>
> - lock_page_cgroup(pc);
> + lock_page_cgroup(pc, flags);
>
> mem = pc->mem_cgroup;
>
> @@ -2219,7 +2225,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
> */
>
> mz = page_cgroup_zoneinfo(pc);
> - unlock_page_cgroup(pc);
> + unlock_page_cgroup(pc, flags);
>
> memcg_check_events(mem, page);
> /* at swapout, this memcg will be accessed to record to swap */
> @@ -2229,7 +2235,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
> return mem;
>
> unlock_out:
> - unlock_page_cgroup(pc);
> + unlock_page_cgroup(pc, flags);
> return NULL;
> }
>
> @@ -2417,17 +2423,18 @@ int mem_cgroup_prepare_migration(struct page *page, struct mem_cgroup **ptr)
> struct page_cgroup *pc;
> struct mem_cgroup *mem = NULL;
> int ret = 0;
> + unsigned long flags;
>
> if (mem_cgroup_disabled())
> return 0;
>
> pc = lookup_page_cgroup(page);
> - lock_page_cgroup(pc);
> + lock_page_cgroup(pc, flags);
> if (PageCgroupUsed(pc)) {
> mem = pc->mem_cgroup;
> css_get(&mem->css);
> }
> - unlock_page_cgroup(pc);
> + unlock_page_cgroup(pc, flags);
>
> if (mem) {
> ret = __mem_cgroup_try_charge(NULL, GFP_KERNEL, &mem, false);
> --
> 1.6.4
>
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