On Fri 06-05-16 09:04:34, Dave Hansen wrote: > On 05/06/2016 08:10 AM, Odzioba, Lukasz wrote: > > On Thu 05-05-16 09:21:00, Michal Hocko wrote: > >> Or maybe the async nature of flushing turns > >> out to be just impractical and unreliable and we will end up skipping > >> THP (or all compound pages) for pcp LRU add cache. Let's see... > > > > What if we simply skip lru_add pvecs for compound pages? > > That way we still have compound pages on LRU's, but the problem goes > > away. It is not quite what this naïve patch does, but it works nice for me. > > > > diff --git a/mm/swap.c b/mm/swap.c > > index 03aacbc..c75d5e1 100644 > > --- a/mm/swap.c > > +++ b/mm/swap.c > > @@ -392,7 +392,9 @@ static void __lru_cache_add(struct page *page) > > get_page(page); > > if (!pagevec_space(pvec)) > > __pagevec_lru_add(pvec); > > pagevec_add(pvec, page); > > + if (PageCompound(page)) > > + __pagevec_lru_add(pvec); > > put_cpu_var(lru_add_pvec); > > } > > That's not _quite_ what I had in mind since that drains the entire pvec > every time a large page is encountered. But I'm conflicted about what > the right behavior _is_. > > We'd taking the LRU lock for 'page' anyway, so we might as well drain > the pvec. Yes I think this makes sense. The only case where it would be suboptimal is when the pagevec was already full and then we just created a single page pvec to drain it. This can be handled better though by: diff --git a/mm/swap.c b/mm/swap.c index 95916142fc46..3fe4f180e8bf 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -391,9 +391,8 @@ static void __lru_cache_add(struct page *page) struct pagevec *pvec = &get_cpu_var(lru_add_pvec); get_page(page); - if (!pagevec_space(pvec)) + if (!pagevec_add(pvec, page) || PageCompound(page)) __pagevec_lru_add(pvec); - pagevec_add(pvec, page); put_cpu_var(lru_add_pvec); } > Or, does the additional work to put the page on to a pvec and then > immediately drain it overwhelm that advantage? pagevec_add is quite trivial so I would be really surprised if it mattered. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>