Re: [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.