| Message ID | 1604566549-62481-8-git-send-email-alex.shi@linux.alibaba.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | per memcg lru lock | expand |
On Thu, Nov 05, 2020 at 04:55:37PM +0800, Alex Shi wrote: > From: Hugh Dickins <hughd@google.com> > > It is necessary for page_idle_get_page() to recheck PageLRU() after > get_page_unless_zero(), but holding lru_lock around that serves no > useful purpose, and adds to lru_lock contention: delete it. > > See https://lore.kernel.org/lkml/20150504031722.GA2768@blaptop for the > discussion that led to lru_lock there; but __page_set_anon_rmap() now > uses WRITE_ONCE(), and I see no other risk in page_idle_clear_pte_refs() > using rmap_walk() (beyond the risk of racing PageAnon->PageKsm, mostly > but not entirely prevented by page_count() check in ksm.c's > write_protect_page(): that risk being shared with page_referenced() and > not helped by lru_lock). > > Signed-off-by: Hugh Dickins <hughd@google.com> > Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Vladimir Davydov <vdavydov.dev@gmail.com> > Cc: Vlastimil Babka <vbabka@suse.cz> > Cc: Minchan Kim <minchan@kernel.org> > Cc: Alex Shi <alex.shi@linux.alibaba.com> > Cc: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org Acked-by: Johannes Weiner <hannes@cmpxchg.org>
On Thu, Nov 5, 2020 at 4:56 PM Alex Shi <alex.shi@linux.alibaba.com> wrote: > > From: Hugh Dickins <hughd@google.com> > > It is necessary for page_idle_get_page() to recheck PageLRU() after > get_page_unless_zero(), but holding lru_lock around that serves no > useful purpose, and adds to lru_lock contention: delete it. > > See https://lore.kernel.org/lkml/20150504031722.GA2768@blaptop for the > discussion that led to lru_lock there; but __page_set_anon_rmap() now > uses WRITE_ONCE(), and I see no other risk in page_idle_clear_pte_refs() > using rmap_walk() (beyond the risk of racing PageAnon->PageKsm, mostly > but not entirely prevented by page_count() check in ksm.c's > write_protect_page(): that risk being shared with page_referenced() and > not helped by lru_lock). > > Signed-off-by: Hugh Dickins <hughd@google.com> > Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Vladimir Davydov <vdavydov.dev@gmail.com> > Cc: Vlastimil Babka <vbabka@suse.cz> > Cc: Minchan Kim <minchan@kernel.org> > Cc: Alex Shi <alex.shi@linux.alibaba.com> > Cc: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org > --- > mm/page_idle.c | 4 ---- > 1 file changed, 4 deletions(-) > > diff --git a/mm/page_idle.c b/mm/page_idle.c > index 057c61df12db..64e5344a992c 100644 > --- a/mm/page_idle.c > +++ b/mm/page_idle.c > @@ -32,19 +32,15 @@ > static struct page *page_idle_get_page(unsigned long pfn) > { > struct page *page = pfn_to_online_page(pfn); > - pg_data_t *pgdat; > > if (!page || !PageLRU(page) || > !get_page_unless_zero(page)) > return NULL; > > - pgdat = page_pgdat(page); > - spin_lock_irq(&pgdat->lru_lock); get_page_unless_zero() is a full memory barrier. But do we need a compiler barrier here to prevent the compiler to cache PageLRU() results here? Otherwise looks OK to me, Acked-by: "Huang, Ying" <ying.huang@intel.com> Best Regards, Huang, Ying > if (unlikely(!PageLRU(page))) { > put_page(page); > page = NULL; > } > - spin_unlock_irq(&pgdat->lru_lock); > return page; > } > > -- > 1.8.3.1 > >
On 11/11/20 9:17 AM, huang ying wrote: > On Thu, Nov 5, 2020 at 4:56 PM Alex Shi <alex.shi@linux.alibaba.com> wrote: >> >> From: Hugh Dickins <hughd@google.com> >> >> It is necessary for page_idle_get_page() to recheck PageLRU() after >> get_page_unless_zero(), but holding lru_lock around that serves no >> useful purpose, and adds to lru_lock contention: delete it. >> >> See https://lore.kernel.org/lkml/20150504031722.GA2768@blaptop for the >> discussion that led to lru_lock there; but __page_set_anon_rmap() now >> uses WRITE_ONCE(), and I see no other risk in page_idle_clear_pte_refs() >> using rmap_walk() (beyond the risk of racing PageAnon->PageKsm, mostly >> but not entirely prevented by page_count() check in ksm.c's >> write_protect_page(): that risk being shared with page_referenced() and >> not helped by lru_lock). >> >> Signed-off-by: Hugh Dickins <hughd@google.com> >> Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com> >> Cc: Andrew Morton <akpm@linux-foundation.org> >> Cc: Vladimir Davydov <vdavydov.dev@gmail.com> >> Cc: Vlastimil Babka <vbabka@suse.cz> >> Cc: Minchan Kim <minchan@kernel.org> >> Cc: Alex Shi <alex.shi@linux.alibaba.com> >> Cc: linux-mm@kvack.org >> Cc: linux-kernel@vger.kernel.org >> --- >> mm/page_idle.c | 4 ---- >> 1 file changed, 4 deletions(-) >> >> diff --git a/mm/page_idle.c b/mm/page_idle.c >> index 057c61df12db..64e5344a992c 100644 >> --- a/mm/page_idle.c >> +++ b/mm/page_idle.c >> @@ -32,19 +32,15 @@ >> static struct page *page_idle_get_page(unsigned long pfn) >> { >> struct page *page = pfn_to_online_page(pfn); >> - pg_data_t *pgdat; >> >> if (!page || !PageLRU(page) || >> !get_page_unless_zero(page)) >> return NULL; >> >> - pgdat = page_pgdat(page); >> - spin_lock_irq(&pgdat->lru_lock); > > get_page_unless_zero() is a full memory barrier. But do we need a > compiler barrier here to prevent the compiler to cache PageLRU() > results here? Otherwise looks OK to me, I think the compiler barrier is also implied by the full memory barrier and prevents the caching. Acked-by: Vlastimil Babka <vbabka@suse.cz> > Acked-by: "Huang, Ying" <ying.huang@intel.com> > > Best Regards, > Huang, Ying > >> if (unlikely(!PageLRU(page))) { >> put_page(page); >> page = NULL; >> } >> - spin_unlock_irq(&pgdat->lru_lock); >> return page; >> } >> >> -- >> 1.8.3.1 >> >> >
diff --git a/mm/page_idle.c b/mm/page_idle.c index 057c61df12db..64e5344a992c 100644 --- a/mm/page_idle.c +++ b/mm/page_idle.c @@ -32,19 +32,15 @@ static struct page *page_idle_get_page(unsigned long pfn) { struct page *page = pfn_to_online_page(pfn); - pg_data_t *pgdat; if (!page || !PageLRU(page) || !get_page_unless_zero(page)) return NULL; - pgdat = page_pgdat(page); - spin_lock_irq(&pgdat->lru_lock); if (unlikely(!PageLRU(page))) { put_page(page); page = NULL; } - spin_unlock_irq(&pgdat->lru_lock); return page; }