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-rw-r--r--mm/vmscan.c33
1 files changed, 24 insertions, 9 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c
index ca43aa0..e37e687 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -723,23 +723,38 @@ static unsigned long shrink_page_list(struct list_head *page_list,
/*
* memcg doesn't have any dirty pages throttling so we
* could easily OOM just because too many pages are in
- * writeback from reclaim and there is nothing else to
- * reclaim.
+ * writeback and there is nothing else to reclaim.
*
- * Check may_enter_fs, certainly because a loop driver
+ * Check __GFP_IO, certainly because a loop driver
* thread might enter reclaim, and deadlock if it waits
* on a page for which it is needed to do the write
* (loop masks off __GFP_IO|__GFP_FS for this reason);
* but more thought would probably show more reasons.
+ *
+ * Don't require __GFP_FS, since we're not going into
+ * the FS, just waiting on its writeback completion.
+ * Worryingly, ext4 gfs2 and xfs allocate pages with
+ * grab_cache_page_write_begin(,,AOP_FLAG_NOFS), so
+ * testing may_enter_fs here is liable to OOM on them.
*/
- if (!global_reclaim(sc) && PageReclaim(page) &&
- may_enter_fs)
- wait_on_page_writeback(page);
- else {
+ if (global_reclaim(sc) ||
+ !PageReclaim(page) || !(sc->gfp_mask & __GFP_IO)) {
+ /*
+ * This is slightly racy - end_page_writeback()
+ * might have just cleared PageReclaim, then
+ * setting PageReclaim here end up interpreted
+ * as PageReadahead - but that does not matter
+ * enough to care. What we do want is for this
+ * page to have PageReclaim set next time memcg
+ * reclaim reaches the tests above, so it will
+ * then wait_on_page_writeback() to avoid OOM;
+ * and it's also appropriate in global reclaim.
+ */
+ SetPageReclaim(page);
nr_writeback++;
- unlock_page(page);
- goto keep;
+ goto keep_locked;
}
+ wait_on_page_writeback(page);
}
references = page_check_references(page, sc);
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