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From: Yu Zhao <yuzhao@google.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Linux-MM <linux-mm@kvack.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Hugh Dickins <hughd@google.com>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	Matthew Wilcox <willy@infradead.org>,
	Vlastimil Babka <vbabka@suse.cz>, Yang Shi <shy828301@gmail.com>,
	Zi Yan <ziy@nvidia.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Shuang Zhai <zhais@google.com>
Subject: Re: [PATCH 2/3] mm: free zapped tail pages when splitting isolated thp
Date: Sun, 8 Aug 2021 11:28:37 -0600	[thread overview]
Message-ID: <CAOUHufZfMTi6_V_hw26WXapMpUuFgT6qnupYkcmkz=qGBWwHsw@mail.gmail.com> (raw)
In-Reply-To: <20210804142257.tsgzpfc3zq7um7iu@box.shutemov.name>

On Wed, Aug 4, 2021 at 8:22 AM Kirill A. Shutemov <kirill@shutemov.name> wrote:
>
> On Sat, Jul 31, 2021 at 12:39:37AM -0600, Yu Zhao wrote:
> > @@ -2506,6 +2508,25 @@ static void __split_huge_page(struct page *page, struct list_head *list,
> >                       continue;
> >               unlock_page(subpage);
> >
> > +             /*
> > +              * If a tail page has only two references left, one inherited
> > +              * from the isolation of its head and the other from
> > +              * lru_add_page_tail() which we are about to drop, it means this
> > +              * tail page was concurrently zapped. Then we can safely free it
> > +              * and save page reclaim or migration the trouble of trying it.
> > +              */
> > +             if (list && page_ref_freeze(subpage, 2)) {
> > +                     VM_BUG_ON_PAGE(PageLRU(subpage), subpage);
> > +                     VM_BUG_ON_PAGE(PageCompound(subpage), subpage);
> > +                     VM_BUG_ON_PAGE(page_mapped(subpage), subpage);
> > +
> > +                     ClearPageActive(subpage);
> > +                     ClearPageUnevictable(subpage);
>
> Why touch PG_Active/PG_Unevictable?

Subpages may inherit these flags from their isolated head. Page
reclaim doesn't isolate active or unevictable. But migration does. If
we don't clear them here, we'll hit bad_page() later because both
flags are included in PAGE_FLAGS_CHECK_AT_FREE. Does it make sense?
Thanks.

  reply	other threads:[~2021-08-08 17:28 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-31  6:39 [PATCH 0/3] mm: optimize thp for reclaim and migration Yu Zhao
2021-07-31  6:39 ` [PATCH 1/3] mm: don't take lru lock when splitting isolated thp Yu Zhao
2021-07-31  6:39 ` [PATCH 2/3] mm: free zapped tail pages " Yu Zhao
2021-08-04 14:22   ` Kirill A. Shutemov
2021-08-08 17:28     ` Yu Zhao [this message]
2021-08-05  0:13   ` Yang Shi
2021-08-08 17:49     ` Yu Zhao
2021-08-11 22:25       ` Yang Shi
2021-08-11 23:12         ` Yu Zhao
2021-08-13 23:24           ` Yang Shi
2021-08-13 23:56             ` Yu Zhao
2021-08-14  0:30               ` Yang Shi
2021-08-14  1:49                 ` Yu Zhao
2021-08-14  2:34                   ` Yang Shi
2021-07-31  6:39 ` [PATCH 3/3] mm: don't remap clean subpages " Yu Zhao
2021-07-31  9:53   ` kernel test robot
2021-07-31 15:45   ` kernel test robot
2021-08-03 11:25   ` Matthew Wilcox
2021-08-03 11:36   ` Matthew Wilcox
2021-08-08 17:21     ` Yu Zhao
2021-08-04 14:27   ` Kirill A. Shutemov

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