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    SubjectRe: [PATCH V4 3/6] mm: move MADV_FREE pages into LRU_INACTIVE_FILE list
    On Thu, Feb 23, 2017 at 08:26:03AM -0800, Shaohua Li wrote:
    > On Thu, Feb 23, 2017 at 10:58:27AM -0500, Johannes Weiner wrote:
    > > Hi Shaohua,
    > >
    > > On Wed, Feb 22, 2017 at 10:50:41AM -0800, Shaohua Li wrote:
    > > > @@ -268,6 +268,12 @@ static void __activate_page(struct page *page, struct lruvec *lruvec,
    > > > int lru = page_lru_base_type(page);
    > > >
    > > > del_page_from_lru_list(page, lruvec, lru);
    > > > + if (PageAnon(page) && !PageSwapBacked(page)) {
    > > > + SetPageSwapBacked(page);
    > > > + /* charge to anon scanned/rotated reclaim_stat */
    > > > + file = 0;
    > > > + lru = LRU_INACTIVE_ANON;
    > > > + }
    > >
    > > As per my previous feedback, please remove this. Write-after-free will
    > > be caught and handled in the reclaimer, read-after-free is a bug that
    > > really doesn't require optimizing page aging for. And we definitely
    > > shouldn't declare invalid data suddenly valid because it's being read.
    >
    > GUP could run into this. Don't we move the page because it's hot? I think it's
    > not just about page aging. If we leave the page there, page reclaim will just
    > waste time to reclaim the pages which should't be reclaimed.

    There is just no convincing justification to add this code, because it
    optimizes something that doesn't have a real world application. If we
    just delete this branch, for all intents and purposes the outcome will
    be perfectly acceptable.

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