ext4 crypto: allocate bounce pages using GFP_NOWAIT

Previously we allocated bounce pages using a combination of
alloc_page() and mempool_alloc() with the __GFP_WAIT bit set.
Instead, use mempool_alloc() with GFP_NOWAIT.  The mempool_alloc()
function will try using alloc_pages() initially, and then only use the
mempool reserve of pages if alloc_pages() is unable to fulfill the
request.

This minimizes the the impact on the mm layer when we need to do a
large amount of writeback of encrypted files, as Jaeguk Kim had
reported that under a heavy fio workload on a system with restricted
amounts memory (which unfortunately, includes many mobile handsets),
he had observed the the OOM killer getting triggered several times.
Using GFP_NOWAIT

If the mempool_alloc() function fails, we will retry the page
writeback at a later time; the function of the mempool is to ensure
that we can writeback at least 32 pages at a time, so we can more
efficiently dispatch I/O under high memory pressure situations.  In
the future we should make this be a tunable so we can determine the
best tradeoff between permanently sequestering memory and the ability
to quickly launder pages so we can free up memory quickly when
necessary.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 1 insertions, 2 deletions

diff --git a/fs/ext4/ext4_crypto.h b/fs/ext4/ext4_crypto.h
index 34e0d24..ac7d4e8 100644
--- a/fs/ext4/ext4_crypto.h
+++ b/fs/ext4/ext4_crypto.h
@@ -83,8 +83,7 @@ struct ext4_crypt_info {
 };
 
 #define EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL             0x00000001
-#define EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL     0x00000002
-#define EXT4_WRITE_PATH_FL			      0x00000004
+#define EXT4_WRITE_PATH_FL			      0x00000002
 
 struct ext4_crypto_ctx {
 	union {