allocate-bounce-pages-using-gfp-nowait

   1 ext4 crypto: allocate bounce pages using GFP_NOWAIT
   2
   3 Previously we allocated bounce pages using a combination of
   4 alloc_page() and mempool_alloc() with the __GFP_WAIT bit set.
   5 Instead, use mempool_alloc() with GFP_NOWAIT.  The mempool_alloc()
   6 function will try using alloc_pages() initially, and then only use the
   7 mempool reserve of pages if alloc_pages() is unable to fulfill the
   8 request.
   9
  10 This minimizes the the impact on the mm layer when we need to do a
  11 large amount of writeback of encrypted files, as Jaeguk Kim had
  12 reported that under a heavy fio workload on a system with restricted
  13 amounts memory (which unfortunately, includes many mobile handsets),
  14 he had observed the the OOM killer getting triggered several times.
  15 Using GFP_NOWAIT
  16
  17 If the mempool_alloc() function fails, we will retry the page
  18 writeback at a later time; the function of the mempool is to ensure
  19 that we can writeback at least 32 pages at a time, so we can more
  20 efficiently dispatch I/O under high memory pressure situations.  In
  21 the future we should make this be a tunable so we can determine the
  22 best tradeoff between permanently sequestering memory and the ability
  23 to quickly launder pages so we can free up memory quickly when
  24 necessary.
  25
  26 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
  27 ---
  28  fs/ext4/crypto.c      | 27 ++++++---------------------
  29  fs/ext4/ext4_crypto.h |  3 +--
  30  2 files changed, 7 insertions(+), 23 deletions(-)
  31
  32 diff --git a/fs/ext4/crypto.c b/fs/ext4/crypto.c
  33 index efcb7c0..f5c82e8 100644
  34 --- a/fs/ext4/crypto.c
  35 +++ b/fs/ext4/crypto.c
  36 @@ -71,12 +71,8 @@ void ext4_release_crypto_ctx(struct ext4_crypto_ctx *ctx)
  37  {
  38         unsigned long flags;
  39
  40 -       if (ctx->flags & EXT4_WRITE_PATH_FL && ctx->w.bounce_page) {
  41 -               if (ctx->flags & EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL)
  42 -                       __free_page(ctx->w.bounce_page);
  43 -               else
  44 -                       mempool_free(ctx->w.bounce_page, ext4_bounce_page_pool);
  45 -       }
  46 +       if (ctx->flags & EXT4_WRITE_PATH_FL && ctx->w.bounce_page)
  47 +               mempool_free(ctx->w.bounce_page, ext4_bounce_page_pool);
  48         ctx->w.bounce_page = NULL;
  49         ctx->w.control_page = NULL;
  50         if (ctx->flags & EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL) {
  51 @@ -317,22 +313,11 @@ static int ext4_page_crypto(struct ext4_crypto_ctx *ctx,
  52
  53  static struct page *alloc_bounce_page(struct ext4_crypto_ctx *ctx)
  54  {
  55 -       struct page *ciphertext_page = alloc_page(GFP_NOFS);
  56 -
  57 -       if (!ciphertext_page) {
  58 -               /* This is a potential bottleneck, but at least we'll have
  59 -                * forward progress. */
  60 -               ciphertext_page = mempool_alloc(ext4_bounce_page_pool,
  61 -                                                GFP_NOFS);
  62 -               if (ciphertext_page == NULL)
  63 -                       return ERR_PTR(-ENOMEM);
  64 -               ctx->flags &= ~EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL;
  65 -       } else {
  66 -               ctx->flags |= EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL;
  67 -       }
  68 +       ctx->w.bounce_page = mempool_alloc(ext4_bounce_page_pool, GFP_NOWAIT);
  69 +       if (ctx->w.bounce_page == NULL)
  70 +               return ERR_PTR(-ENOMEM);
  71         ctx->flags |= EXT4_WRITE_PATH_FL;
  72 -       ctx->w.bounce_page = ciphertext_page;
  73 -       return ciphertext_page;
  74 +       return ctx->w.bounce_page;
  75  }
  76
  77  /**
  78 diff --git a/fs/ext4/ext4_crypto.h b/fs/ext4/ext4_crypto.h
  79 index 34e0d24..ac7d4e8 100644
  80 --- a/fs/ext4/ext4_crypto.h
  81 +++ b/fs/ext4/ext4_crypto.h
  82 @@ -83,8 +83,7 @@ struct ext4_crypt_info {
  83  };
  84
  85  #define EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL             0x00000001
  86 -#define EXT4_BOUNCE_PAGE_REQUIRES_FREE_ENCRYPT_FL     0x00000002
  87 -#define EXT4_WRITE_PATH_FL                           0x00000004
  88 +#define EXT4_WRITE_PATH_FL                           0x00000002
  89
  90  struct ext4_crypto_ctx {
  91         union {