On 2016/6/21 23:29, Kirill A. Shutemov wrote:

On Tue, Jun 21, 2016 at 11:19:07PM +0800, zhong jiang wrote:

quoted

On 2016/6/21 22:37, Kirill A. Shutemov wrote:

quoted

On Tue, Jun 21, 2016 at 10:05:56PM +0800, zhongjiang wrote:

quoted

From: zhong jiang <redacted>

with great pressure, I run some test cases. As a result, I found
that the THP is not freed, it is detected by check_mm().

BUG: Bad rss-counter state mm:ffff8827edb70000 idx:1 val:512

Consider the following race :

	CPU0                               CPU1
  __handle_mm_fault()
        wp_huge_pmd()
   	    do_huge_pmd_wp_page()
		pmdp_huge_clear_flush_notify()
                (pmd_none = true)
					exit_mmap()
					   unmap_vmas()
					     zap_pmd_range()
						pmd_none_or_trans_huge_or_clear_bad()
						   (result in memory leak)
                set_pmd_at()

because of CPU0 have allocated huge page before pmdp_huge_clear_notify,
and it make the pmd entry to be null. Therefore, The memory leak can occur.

The patch fix the scenario that the pmd entry can lead to be null.

I don't think the scenario is possible.

exit_mmap() called when all mm users have gone, so no parallel threads
exist.

 Forget  this patch.  It 's my fault , it indeed don not exist.
 But I  hit the following problem.  we can see the memory leak when the process exit.
 
 
 Any suggestion will be apprecaited.

Could you try this:

http://lkml.kernel.org/r/20160621150433.GA7536@node.shutemov.name

 The patch I have seen ,  but I  don not think this patch  can fix so problem . if that race occur,  pmd entry points to
 the huge page will be changed ,  and freeze_page spilt pmd will fail. subsequent vm_bug_on() will fired.

 freeze_page()
     try_to_unmap()
         split_huge_pmd_address() (return fail) result in page_mapcount is not zero
 vm_bug_on()

               
             

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