Re: [PATCH] mm: call into direct reclaim without PF_MEMALLOC set

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Wed, 2006-11-15 at 13:23 -0800, Andrew Morton wrote:

> spose so.  It assume that current->reclaim_state is NULL if !PF_MEMALLOC
> which I guess is true.
> 
> But do we need to set current->reclaim_state at all in here?

I did a quick grep before sending this out, and thought code assumed
current->reclaim_state was !NULL, however on closer inspection this
seems not so.

*sigh* another version - almost hitting the DaveJ barrier:
  revisions > LOC

---

PF_MEMALLOC is also used to prevent recursion of direct reclaim.
However this invocation does not set PF_MEMALLOC nor checks it and
hence a can make it nest a single time. Either by reaching this
spot from reclaim and then calling it again or entering here and 
encountering a __GFP_WAIT alloc from within.

So check for PF_MEMALLOC and avoid a second invocation and otherwise
set PF_MEMALLOC.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
 fs/buffer.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Index: linux-2.6-git/fs/buffer.c
===================================================================
--- linux-2.6-git.orig/fs/buffer.c	2006-11-15 20:32:14.000000000 +0100
+++ linux-2.6-git/fs/buffer.c	2006-11-15 22:28:43.000000000 +0100
@@ -360,8 +360,11 @@ static void free_more_memory(void)
 
 	for_each_online_pgdat(pgdat) {
 		zones = pgdat->node_zonelists[gfp_zone(GFP_NOFS)].zones;
-		if (*zones)
+		if (*zones && !(current->flags & PF_MEMALLOC)) {
+			current->flags |= PF_MEMALLOC;
 			try_to_free_pages(zones, GFP_NOFS);
+			current->flags &= ~PF_MEMALLOC;
+		}
 	}
 }
 


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