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 efcb7c0..f5c82e8 100644
--- a/fs/ext4/crypto.c
+++ b/fs/ext4/crypto.c
@@ -71,12 +71,8 @@
{
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 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;
}
/**