shmem: fix init_page_accessed use to stop !PageLRU bug

Under shmem swapping load, I sometimes hit the VM_BUG_ON_PAGE(!PageLRU)
in isolate_lru_pages() at mm/vmscan.c:1281!

Commit 2457aec63745 ("mm: non-atomically mark page accessed during page
cache allocation where possible") looks like interrupted work-in-progress.

mm/filemap.c's call to init_page_accessed() is fine, but not mm/shmem.c's
- shmem_write_begin() is clearly wrong to use it after shmem_getpage(),
when the page is always visible in radix_tree, and often already on LRU.

Revert change to shmem_write_begin(), and use init_page_accessed() or
mark_page_accessed() appropriately for SGP_WRITE in shmem_getpage_gfp().

SGP_WRITE also covers shmem_symlink(), which did not mark_page_accessed()
before; but since many other filesystems use [__]page_symlink(), which did
and does mark the page accessed, consider this as rectifying an oversight.

Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Prabhakar Lad <prabhakar.csengg@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/shmem.c b/mm/shmem.c
index 8f419cf..1140f49 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1029,6 +1029,9 @@ repeat:
                goto failed;
        }
 
+       if (page && sgp == SGP_WRITE)
+               mark_page_accessed(page);
+
        /* fallocated page? */
        if (page && !PageUptodate(page)) {
                if (sgp != SGP_READ)
@@ -1110,6 +1113,9 @@ repeat:
                shmem_recalc_inode(inode);
                spin_unlock(&info->lock);
 
+               if (sgp == SGP_WRITE)
+                       mark_page_accessed(page);
+
                delete_from_swap_cache(page);
                set_page_dirty(page);
                swap_free(swap);
@@ -1136,6 +1142,9 @@ repeat:
 
                __SetPageSwapBacked(page);
                __set_page_locked(page);
+               if (sgp == SGP_WRITE)
+                       init_page_accessed(page);
+
                error = mem_cgroup_charge_file(page, current->mm,
                                                gfp & GFP_RECLAIM_MASK);
                if (error)
@@ -1412,13 +1421,9 @@ shmem_write_begin(struct file *file, struct address_space *mapping,
                        loff_t pos, unsigned len, unsigned flags,
                        struct page **pagep, void **fsdata)
 {
-       int ret;
        struct inode *inode = mapping->host;
        pgoff_t index = pos >> PAGE_CACHE_SHIFT;
-       ret = shmem_getpage(inode, index, pagep, SGP_WRITE, NULL);
-       if (ret == 0 && *pagep)
-               init_page_accessed(*pagep);
-       return ret;
+       return shmem_getpage(inode, index, pagep, SGP_WRITE, NULL);
 }
 
 static int