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ext4 crypto: allocate bounce pages using GFP_NOWAIT

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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>
This commit is contained in:
Theodore Ts'o 2015-06-03 09:32:39 -04:00
parent e298e73bd7
commit 3dbb5eb9a3
2 changed files with 7 additions and 23 deletions
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27
fs/ext4/crypto.c
View file

@ -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;
}
/**

3
fs/ext4/ext4_crypto.h
View file

@ -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 {