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    Subject[PATCH 4/6] EXT4: remove congestion_wait from ext4_bio_write_page, and simplify
    congestion_wait() is indistinguishable from
    schedule_timeout_uninterruptible(). It is best avoided and should be
    deprecated.

    It is not needed in ext4_bio_write_page(). There are two cases.
    If there are no ->io_bio yet, then it is appropriate to use __GFP_NOFAIL
    which does the waiting in a better place. The code already uses this
    flag on the second attempt. This patch changes to it always use that
    flag for this case.

    If there *are* ->io_bio (in which case the allocation was non-blocking)
    we submit the io and return the first case. No waiting is needed in
    this case.

    So remove the congestion_wait() call, and simplify the code so that the
    two cases are somewhat clearer.

    Remove the "if (io->io_bio)" before calling ext4_io_submit() as that
    test is performed internally by that function.

    Signed-off-by: NeilBrown <neilb@suse.de>
    ---
    fs/ext4/page-io.c | 13 +++++--------
    1 file changed, 5 insertions(+), 8 deletions(-)

    diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
    index f038d578d8d8..3b6ece0d3ad6 100644
    --- a/fs/ext4/page-io.c
    +++ b/fs/ext4/page-io.c
    @@ -506,7 +506,7 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
    * can't happen in the common case of blocksize == PAGE_SIZE.
    */
    if (fscrypt_inode_uses_fs_layer_crypto(inode) && nr_to_submit) {
    - gfp_t gfp_flags = GFP_NOFS;
    + gfp_t gfp_flags;
    unsigned int enc_bytes = round_up(len, i_blocksize(inode));

    /*
    @@ -514,21 +514,18 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
    * a waiting mask (i.e. request guaranteed allocation) on the
    * first page of the bio. Otherwise it can deadlock.
    */
    + retry_encrypt:
    if (io->io_bio)
    gfp_flags = GFP_NOWAIT | __GFP_NOWARN;
    - retry_encrypt:
    + else
    + gfp_flags = GFP_NOFS | __GFP_NOFAIL;
    bounce_page = fscrypt_encrypt_pagecache_blocks(page, enc_bytes,
    0, gfp_flags);
    if (IS_ERR(bounce_page)) {
    ret = PTR_ERR(bounce_page);
    if (ret == -ENOMEM &&
    (io->io_bio || wbc->sync_mode == WB_SYNC_ALL)) {
    - gfp_flags = GFP_NOFS;
    - if (io->io_bio)
    - ext4_io_submit(io);
    - else
    - gfp_flags |= __GFP_NOFAIL;
    - congestion_wait(BLK_RW_ASYNC, HZ/50);
    + ext4_io_submit(io);
    goto retry_encrypt;
    }


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