[PATCH 2.6.28?] let GFP_NOFS go to swap again

[Hugh Dickins <hugh@veritas.com>]

In the past, GFP_NOFS (but of course not GFP_NOIO) was allowed to reclaim
by writing to swap.  That got partially broken in 2.6.23, when may_enter_fs
initialization was moved up before the allocation of swap, so its
PageSwapCache test was failing the first time around,

Fix it by setting may_enter_fs when add_to_swap() succeeds with
__GFP_IO.  In fact, check __GFP_IO before calling add_to_swap():
allocating swap we're not ready to use just increases disk seeking.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
---
Perhaps this is too late for 2.6.28: your decision.

 mm/vmscan.c |    3 +++
 1 file changed, 3 insertions(+)

--- 2.6.28-rc4/mm/vmscan.c	2008-10-24 09:28:26.000000000 +0100
+++ linux/mm/vmscan.c	2008-11-12 11:52:44.000000000 +0000
@@ -623,6 +623,8 @@ static unsigned long shrink_page_list(st
 		 * Try to allocate it some swap space here.
 		 */
 		if (PageAnon(page) && !PageSwapCache(page)) {
+			if (!(sc->gfp_mask & __GFP_IO))
+				goto keep_locked;
 			switch (try_to_munlock(page)) {
 			case SWAP_FAIL:		/* shouldn't happen */
 			case SWAP_AGAIN:
@@ -634,6 +636,7 @@ static unsigned long shrink_page_list(st
 			}
 			if (!add_to_swap(page, GFP_ATOMIC))
 				goto activate_locked;
+			may_enter_fs = 1;
 		}
 #endif /* CONFIG_SWAP */
 

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