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SubjectRe: [PATCH] mm/shmem: Do not wait for lock_page() in shmem_unused_huge_shrink()
On Fri, Mar 16, 2018 at 01:13:03PM +0100, Michal Hocko wrote:
> On Fri 16-03-18 13:59:08, Kirill A. Shutemov wrote:
> [..]
> > @@ -498,31 +498,42 @@ static unsigned long shmem_unused_huge_shrink(struct shmem_sb_info *sbinfo,
> > continue;
> > }
> >
> > - page = find_lock_page(inode->i_mapping,
> > + page = find_get_page(inode->i_mapping,
> > (inode->i_size & HPAGE_PMD_MASK) >> PAGE_SHIFT);
> > if (!page)
> > goto drop;
> >
> > + /* No huge page at the end of the file: nothing to split */
> > if (!PageTransHuge(page)) {
> > - unlock_page(page);
> > put_page(page);
> > goto drop;
> > }
> >
> > + /*
> > + * Leave the inode on the list if we failed to lock
> > + * the page at this time.
> > + *
> > + * Waiting for the lock may lead to deadlock in the
> > + * reclaim path.
> > + */
> > + if (!trylock_page(page)) {
> > + put_page(page);
> > + goto leave;
> > + }
>
> Can somebody split the huge page after the PageTransHuge check and
> before we lock it?

Nope. Pin on the page is enough to prevent split.

--
Kirill A. Shutemov

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