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>

diff --git a/fs/ext4/crypto.c b/fs/ext4/crypto.c
index efcb7c04d172ba4eb43cf997964d009a8e0cc903..f5c82e8b7b5ce205b5daabe6bfc6801a2d805848 100644 (file)
--- a/fs/ext4/crypto.c
+++ b/fs/ext4/crypto.c
@@ -71,12 +71,8 @@ void ext4_release_crypto_ctx(struct ext4_crypto_ctx *ctx)
 {
        unsigned long flags;
 
-       if (ctx->flags & EXT4_WRITE_PATH_FL && ctx->w.bounce_page) {
-               if (ctx->flags & EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL)
-                       __free_page(ctx->w.bounce_page);
-               else
-                       mempool_free(ctx->w.bounce_page, ext4_bounce_page_pool);
-       }
+       if (ctx->flags & EXT4_WRITE_PATH_FL && ctx->w.bounce_page)
+               mempool_free(ctx->w.bounce_page, ext4_bounce_page_pool);
        ctx->w.bounce_page = NULL;
        ctx->w.control_page = NULL;
        if (ctx->flags & EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL) {
@@ -317,22 +313,11 @@ static int ext4_page_crypto(struct ext4_crypto_ctx *ctx,
 
 static struct page *alloc_bounce_page(struct ext4_crypto_ctx *ctx)
 {
-       struct page *ciphertext_page = alloc_page(GFP_NOFS);
-
-       if (!ciphertext_page) {
-               /* This is a potential bottleneck, but at least we'll have
-                * forward progress. */
-               ciphertext_page = mempool_alloc(ext4_bounce_page_pool,
-                                                GFP_NOFS);
-               if (ciphertext_page == NULL)
-                       return ERR_PTR(-ENOMEM);
-               ctx->flags &= ~EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL;
-       } else {
-               ctx->flags |= EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL;
-       }
+       ctx->w.bounce_page = mempool_alloc(ext4_bounce_page_pool, GFP_NOWAIT);
+       if (ctx->w.bounce_page == NULL)
+               return ERR_PTR(-ENOMEM);
        ctx->flags |= EXT4_WRITE_PATH_FL;
-       ctx->w.bounce_page = ciphertext_page;
-       return ciphertext_page;
+       return ctx->w.bounce_page;
 }
 
 /**

diff --git a/fs/ext4/ext4_crypto.h b/fs/ext4/ext4_crypto.h
index 34e0d2455881022423314108143002a129028b4b..ac7d4e81379630d2f720ea8d389b8322a784f4cf 100644 (file)
--- 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 {