• David Rientjes's avatar
    mm, thp: fix mapped pages avoiding unevictable list on mlock · b676b293
    David Rientjes authored
    When a transparent hugepage is mapped and it is included in an mlock()
    range, follow_page() incorrectly avoids setting the page's mlock bit and
    moving it to the unevictable lru.
    
    This is evident if you try to mlock(), munlock(), and then mlock() a
    range again.  Currently:
    
    	#define MAP_SIZE	(4 << 30)	/* 4GB */
    
    	void *ptr = mmap(NULL, MAP_SIZE, PROT_READ | PROT_WRITE,
    			 MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
    	mlock(ptr, MAP_SIZE);
    
    		$ grep -E "Unevictable|Inactive\(anon" /proc/meminfo
    		Inactive(anon):     6304 kB
    		Unevictable:     4213924 kB
    
    	munlock(ptr, MAP_SIZE);
    
    		Inactive(anon):  4186252 kB
    		Unevictable:       19652 kB
    
    	mlock(ptr, MAP_SIZE);
    
    		Inactive(anon):  4198556 kB
    		Unevictable:       21684 kB
    
    Notice that less than 2MB was added to the unevictable list; this is
    because these pages in the range are not transparent hugepages since the
    4GB range was allocated with mmap() and has no specific alignment.  If
    posix_memalign() were used instead, unevictable would not have grown at
    all on the second mlock().
    
    The fix is to call mlock_vma_page() so that the mlock bit is set and the
    page is added to the unevictable list.  With this patch:
    
    	mlock(ptr, MAP_SIZE);
    
    		Inactive(anon):     4056 kB
    		Unevictable:     4213940 kB
    
    	munlock(ptr, MAP_SIZE);
    
    		Inactive(anon):  4198268 kB
    		Unevictable:       19636 kB
    
    	mlock(ptr, MAP_SIZE);
    
    		Inactive(anon):     4008 kB
    		Unevictable:     4213940 kB
    Signed-off-by: default avatarDavid Rientjes <rientjes@google.com>
    Acked-by: default avatarHugh Dickins <hughd@google.com>
    Reviewed-by: default avatarAndrea Arcangeli <aarcange@redhat.com>
    Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
    Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Michel Lespinasse <walken@google.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    b676b293
huge_memory.c 63.4 KB