| Message ID | 1584124476-76534-2-git-send-email-yang.shi@linux.alibaba.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/2] mm: swap: make page_evictable() inline | expand |
On 3/13/20 7:34 PM, Yang Shi wrote: > Memory barrier is needed after setting LRU bit, but smp_mb() is too > strong. Some architectures, i.e. x86, imply memory barrier with atomic > operations, so replacing it with smp_mb__after_atomic() sounds better, > which is nop on strong ordered machines, and full memory barriers on > others. With this change the vm-calability cases would perform better > on x86, I saw total 6% improvement with this patch and previous inline > fix. > > The test data (lru-file-readtwice throughput) against v5.6-rc4: > mainline w/ inline fix w/ both (adding this) > 150MB 154MB 159MB > > Fixes: 9c4e6b1a7027 ("mm, mlock, vmscan: no more skipping pagevecs") > Cc: Shakeel Butt <shakeelb@google.com> > Cc: Vlastimil Babka <vbabka@suse.cz> > Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> According to my understanding of Documentation/memory_barriers.txt this would be correct (but it might not say much :) Acked-by: Vlastimil Babka <vbabka@suse.cz> But i have some suggestions... > --- > mm/swap.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/mm/swap.c b/mm/swap.c > index cf39d24..118bac4 100644 > --- a/mm/swap.c > +++ b/mm/swap.c > @@ -945,20 +945,20 @@ static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec, > * #0: __pagevec_lru_add_fn #1: clear_page_mlock > * > * SetPageLRU() TestClearPageMlocked() > - * smp_mb() // explicit ordering // above provides strict > + * MB() // explicit ordering // above provides strict Why MB()? That would be the first appareance of 'MB()' in the whole tree. I think it's fine keeping smp_mb()... > * // ordering > * PageMlocked() PageLRU() > * > * > * if '#1' does not observe setting of PG_lru by '#0' and fails > * isolation, the explicit barrier will make sure that page_evictable > - * check will put the page in correct LRU. Without smp_mb(), SetPageLRU > + * check will put the page in correct LRU. Without MB(), SetPageLRU ... same here ... > * can be reordered after PageMlocked check and can make '#1' to fail > * the isolation of the page whose Mlocked bit is cleared (#0 is also > * looking at the same page) and the evictable page will be stranded > * in an unevictable LRU. Only here I would note that SetPageLRU() is an atomic bitop so we can use the __after_atomic() variant. And I would move the actual SetPageLRU() call from above the comment here right before the barrier. > */ > - smp_mb(); > + smp_mb__after_atomic(); Thanks. > > if (page_evictable(page)) { > lru = page_lru(page); >
On 3/16/20 10:40 AM, Vlastimil Babka wrote: > On 3/13/20 7:34 PM, Yang Shi wrote: >> Memory barrier is needed after setting LRU bit, but smp_mb() is too >> strong. Some architectures, i.e. x86, imply memory barrier with atomic >> operations, so replacing it with smp_mb__after_atomic() sounds better, >> which is nop on strong ordered machines, and full memory barriers on >> others. With this change the vm-calability cases would perform better >> on x86, I saw total 6% improvement with this patch and previous inline >> fix. >> >> The test data (lru-file-readtwice throughput) against v5.6-rc4: >> mainline w/ inline fix w/ both (adding this) >> 150MB 154MB 159MB >> >> Fixes: 9c4e6b1a7027 ("mm, mlock, vmscan: no more skipping pagevecs") >> Cc: Shakeel Butt <shakeelb@google.com> >> Cc: Vlastimil Babka <vbabka@suse.cz> >> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> > According to my understanding of Documentation/memory_barriers.txt this would be > correct (but it might not say much :) This is my understanding too. > > Acked-by: Vlastimil Babka <vbabka@suse.cz> > > But i have some suggestions... > >> --- >> mm/swap.c | 6 +++--- >> 1 file changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/mm/swap.c b/mm/swap.c >> index cf39d24..118bac4 100644 >> --- a/mm/swap.c >> +++ b/mm/swap.c >> @@ -945,20 +945,20 @@ static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec, >> * #0: __pagevec_lru_add_fn #1: clear_page_mlock >> * >> * SetPageLRU() TestClearPageMlocked() >> - * smp_mb() // explicit ordering // above provides strict >> + * MB() // explicit ordering // above provides strict > Why MB()? That would be the first appareance of 'MB()' in the whole tree. I > think it's fine keeping smp_mb()... I would like to use a more general name, maybe just use "memory barrier"? > >> * // ordering >> * PageMlocked() PageLRU() >> * >> * >> * if '#1' does not observe setting of PG_lru by '#0' and fails >> * isolation, the explicit barrier will make sure that page_evictable >> - * check will put the page in correct LRU. Without smp_mb(), SetPageLRU >> + * check will put the page in correct LRU. Without MB(), SetPageLRU > ... same here ... > >> * can be reordered after PageMlocked check and can make '#1' to fail >> * the isolation of the page whose Mlocked bit is cleared (#0 is also >> * looking at the same page) and the evictable page will be stranded >> * in an unevictable LRU. > Only here I would note that SetPageLRU() is an atomic bitop so we can use the > __after_atomic() variant. And I would move the actual SetPageLRU() call from > above the comment here right before the barrier. Sure. Thanks. > >> */ >> - smp_mb(); >> + smp_mb__after_atomic(); > Thanks. > >> >> if (page_evictable(page)) { >> lru = page_lru(page); >>
On 3/16/20 10:49 AM, Yang Shi wrote: > > > On 3/16/20 10:40 AM, Vlastimil Babka wrote: >> On 3/13/20 7:34 PM, Yang Shi wrote: >>> Memory barrier is needed after setting LRU bit, but smp_mb() is too >>> strong. Some architectures, i.e. x86, imply memory barrier with atomic >>> operations, so replacing it with smp_mb__after_atomic() sounds better, >>> which is nop on strong ordered machines, and full memory barriers on >>> others. With this change the vm-calability cases would perform better >>> on x86, I saw total 6% improvement with this patch and previous inline >>> fix. >>> >>> The test data (lru-file-readtwice throughput) against v5.6-rc4: >>> mainline w/ inline fix w/ both (adding this) >>> 150MB 154MB 159MB >>> >>> Fixes: 9c4e6b1a7027 ("mm, mlock, vmscan: no more skipping pagevecs") >>> Cc: Shakeel Butt <shakeelb@google.com> >>> Cc: Vlastimil Babka <vbabka@suse.cz> >>> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> >> According to my understanding of Documentation/memory_barriers.txt >> this would be >> correct (but it might not say much :) > > This is my understanding too. > >> >> Acked-by: Vlastimil Babka <vbabka@suse.cz> >> >> But i have some suggestions... >> >>> --- >>> mm/swap.c | 6 +++--- >>> 1 file changed, 3 insertions(+), 3 deletions(-) >>> >>> diff --git a/mm/swap.c b/mm/swap.c >>> index cf39d24..118bac4 100644 >>> --- a/mm/swap.c >>> +++ b/mm/swap.c >>> @@ -945,20 +945,20 @@ static void __pagevec_lru_add_fn(struct page >>> *page, struct lruvec *lruvec, >>> * #0: __pagevec_lru_add_fn #1: clear_page_mlock >>> * >>> * SetPageLRU() TestClearPageMlocked() >>> - * smp_mb() // explicit ordering // above provides strict >>> + * MB() // explicit ordering // above provides strict >> Why MB()? That would be the first appareance of 'MB()' in the whole >> tree. I >> think it's fine keeping smp_mb()... > > I would like to use a more general name, maybe just use "memory barrier"? Keeping smp_mb() should be just fine... > >> >>> * // ordering >>> * PageMlocked() PageLRU() >>> * >>> * >>> * if '#1' does not observe setting of PG_lru by '#0' and fails >>> * isolation, the explicit barrier will make sure that >>> page_evictable >>> - * check will put the page in correct LRU. Without smp_mb(), >>> SetPageLRU >>> + * check will put the page in correct LRU. Without MB(), >>> SetPageLRU >> ... same here ... >> >>> * can be reordered after PageMlocked check and can make '#1' >>> to fail >>> * the isolation of the page whose Mlocked bit is cleared (#0 >>> is also >>> * looking at the same page) and the evictable page will be >>> stranded >>> * in an unevictable LRU. >> Only here I would note that SetPageLRU() is an atomic bitop so we can >> use the >> __after_atomic() variant. And I would move the actual SetPageLRU() >> call from >> above the comment here right before the barrier. > > Sure. Thanks. > >> >>> */ >>> - smp_mb(); >>> + smp_mb__after_atomic(); >> Thanks. >> >>> if (page_evictable(page)) { >>> lru = page_lru(page); >>> >
diff --git a/mm/swap.c b/mm/swap.c index cf39d24..118bac4 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -945,20 +945,20 @@ static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec, * #0: __pagevec_lru_add_fn #1: clear_page_mlock * * SetPageLRU() TestClearPageMlocked() - * smp_mb() // explicit ordering // above provides strict + * MB() // explicit ordering // above provides strict * // ordering * PageMlocked() PageLRU() * * * if '#1' does not observe setting of PG_lru by '#0' and fails * isolation, the explicit barrier will make sure that page_evictable - * check will put the page in correct LRU. Without smp_mb(), SetPageLRU + * check will put the page in correct LRU. Without MB(), SetPageLRU * can be reordered after PageMlocked check and can make '#1' to fail * the isolation of the page whose Mlocked bit is cleared (#0 is also * looking at the same page) and the evictable page will be stranded * in an unevictable LRU. */ - smp_mb(); + smp_mb__after_atomic(); if (page_evictable(page)) { lru = page_lru(page);
Memory barrier is needed after setting LRU bit, but smp_mb() is too strong. Some architectures, i.e. x86, imply memory barrier with atomic operations, so replacing it with smp_mb__after_atomic() sounds better, which is nop on strong ordered machines, and full memory barriers on others. With this change the vm-calability cases would perform better on x86, I saw total 6% improvement with this patch and previous inline fix. The test data (lru-file-readtwice throughput) against v5.6-rc4: mainline w/ inline fix w/ both (adding this) 150MB 154MB 159MB Fixes: 9c4e6b1a7027 ("mm, mlock, vmscan: no more skipping pagevecs") Cc: Shakeel Butt <shakeelb@google.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> --- mm/swap.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)