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    SubjectRe: [PATCH V2 3/7] mm: reclaim MADV_FREE pages
    On Fri, Feb 10, 2017 at 09:43:07AM -0800, Shaohua Li wrote:

    < snip >

    > > > diff --git a/mm/vmscan.c b/mm/vmscan.c
    > > > index 947ab6f..b304a84 100644
    > > > --- a/mm/vmscan.c
    > > > +++ b/mm/vmscan.c
    > > > @@ -864,7 +864,7 @@ static enum page_references page_check_references(struct page *page,
    > > > return PAGEREF_RECLAIM;
    > > >
    > > > if (referenced_ptes) {
    > > > - if (PageSwapBacked(page))
    > > > + if (PageSwapBacked(page) || PageAnon(page))
    > >
    > > If anyone accesses MADV_FREEed range with load op, not store,
    > > why shouldn't we discard that pages?
    >
    > Don't have strong opinion about this, userspace probably shouldn't do this. I'm
    > ok to delete it if you insist.

    Yes, I prefer to removing unnecessary code unless there is a some reaason.

    >
    > > > return PAGEREF_ACTIVATE;
    > > > /*
    > > > * All mapped pages start out with page table

    < snip >

    > > > @@ -971,7 +971,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
    > > > int may_enter_fs;
    > > > enum page_references references = PAGEREF_RECLAIM_CLEAN;
    > > > bool dirty, writeback;
    > > > - bool lazyfree = false;
    > > > + bool lazyfree;
    > > > int ret = SWAP_SUCCESS;
    > > >
    > > > cond_resched();
    > > > @@ -986,6 +986,8 @@ static unsigned long shrink_page_list(struct list_head *page_list,
    > > >
    > > > sc->nr_scanned++;
    > > >
    > > > + lazyfree = page_is_lazyfree(page);
    > > > +
    > > > if (unlikely(!page_evictable(page)))
    > > > goto cull_mlocked;
    > > >
    > > > @@ -993,7 +995,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
    > > > goto keep_locked;
    > > >
    > > > /* Double the slab pressure for mapped and swapcache pages */
    > > > - if (page_mapped(page) || PageSwapCache(page))
    > > > + if ((page_mapped(page) || PageSwapCache(page)) && !lazyfree)
    > > > sc->nr_scanned++;
    > >
    > > In this phase, we cannot know whether lazyfree marked page is discarable
    > > or not. If it is freeable and mapped, this logic makes sense. However,
    > > if the page is dirty?
    >
    > I think this doesn't matter. If the page is dirty, it will go to reclaim in
    > next round and swap out. At that time, we will add nr_scanned there.

    If the lazyfree page in LRU comes around again into this, it's true but
    the page could be freed before that.
    Having said that, I don't know how critical it is and what kinds of rationale
    was to push slab reclaim so I don't insist on it.

    Thanks.

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