GFS2: Remove a __GFP_NOFAIL allocation

In order to ensure that we've got enough buffer heads for flushing
the journal, the orignal code used __GFP_NOFAIL when performing
this allocation. Here we dispense with that in favour of using a
mempool. This should improve efficiency in low memory conditions
since flushing the journal is a good way to get memory back, we
don't want to be spinning, waiting on memory allocations. The
buffers which are allocated via this mempool are fairly short lived,
so that we'll recycle them pretty quickly.

Although there are other memory allocations which occur during the
journal flush process, this is the one which can potentially require
the most memory, so the most important one to fix.

The amount of memory reserved is a fixed amount, and we should not need
to scale it when there are a greater number of filesystems in use.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/fs/gfs2/lops.c b/fs/gfs2/lops.c
index fe369bd..87e6e0d 100644
--- a/fs/gfs2/lops.c
+++ b/fs/gfs2/lops.c
@@ -12,6 +12,7 @@
 #include <linux/spinlock.h>
 #include <linux/completion.h>
 #include <linux/buffer_head.h>
+#include <linux/mempool.h>
 #include <linux/gfs2_ondisk.h>
 #include <linux/bio.h>
 #include <linux/fs.h>
@@ -199,7 +200,7 @@ static void gfs2_fake_write_endio(struct buffer_head *bh, int uptodate)
 	struct gfs2_sbd *sdp = bd->bd_gl->gl_sbd;
 
 	end_buffer_write_sync(bh, uptodate);
-	free_buffer_head(bh);
+	mempool_free(bh, gfs2_bh_pool);
 	unlock_buffer(real_bh);
 	brelse(real_bh);
 	if (atomic_dec_and_test(&sdp->sd_log_in_flight))
@@ -220,7 +221,7 @@ static struct buffer_head *gfs2_log_fake_buf(struct gfs2_sbd *sdp,
 	u64 blkno = gfs2_log_bmap(sdp, sdp->sd_log_flush_head);
 	struct buffer_head *bh;
 
-	bh = alloc_buffer_head(GFP_NOFS | __GFP_NOFAIL);
+	bh = mempool_alloc(gfs2_bh_pool, GFP_NOFS);
 	atomic_set(&bh->b_count, 1);
 	bh->b_state = (1 << BH_Mapped) | (1 << BH_Uptodate) | (1 << BH_Lock);
 	set_bh_page(bh, real->b_page, bh_offset(real));