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List: linux-ext4
Subject: Re: [PATCH] Ext4: Don't normalize an falloc request if it can fit
From: Ted Ts'o <tytso () mit ! edu>
Date: 2011-10-31 22:42:34
Message-ID: 20111031224234.GP16825 () thunk ! org
[Download RAW message or body]
On Fri, Oct 28, 2011 at 11:01:57AM -0700, Greg Harm wrote:
> If an fallocate request fits in EXT_UNINIT_MAX_LEN, then set the
> EXT4_GET_BLOCKS_NO_NORMALIZE flag. For larger fallocate requests,
> let mballoc.c normalize the request.
> This fixes a problem where large requests were being split
> into non-contiguous extents due to haldar@google.com's
> "ext4: do not normalize block requests from fallocate."
>
> Testing: Checked that 8.x MB falloc'ed files are still laid down
> next to each other (contiguously).
> Checked that the maximum size extent (127.9MB) is allocated as 1
> extent.
> Checked that a 1GB file is somewhat contiguous (often 5-6
> non-contiguous extents now).
> Checked that a 120MB file can still be falloc'ed even if there are no
> single extents large enough to hold it.
>
> Signed-off-by: Greg Harm <gharm@google.com>
Thanks, I had to tweak the patch slightly to make it apply given the
current ext4 tree.
- Ted
commit 5f11e7c457769808bafe5048a98c5cfd624e85f3
Author: Greg Harm <gharm@google.com>
Date: Mon Oct 31 18:41:47 2011 -0400
ext4: Don't normalize an falloc request if it can fit in 1 extent.
If an fallocate request fits in EXT_UNINIT_MAX_LEN, then set the
EXT4_GET_BLOCKS_NO_NORMALIZE flag. For larger fallocate requests,
let mballoc.c normalize the request.
This fixes a problem where large requests were being split into
non-contiguous extents due to commit 556b27abf73: ext4: do not
normalize block requests from fallocate.
Testing:
*) Checked that 8.x MB falloc'ed files are still laid down next to
each other (contiguously).
*) Checked that the maximum size extent (127.9MB) is allocated as 1
extent.
*) Checked that a 1GB file is somewhat contiguous (often 5-6
non-contiguous extents now).
*) Checked that a 120MB file can still be falloc'ed even if there are
no single extents large enough to hold it.
Signed-off-by: Greg Harm <gharm@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index e585caa..9dfdf8f 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4336,10 +4336,16 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
trace_ext4_fallocate_exit(inode, offset, max_blocks, ret);
return ret;
}
- flags = EXT4_GET_BLOCKS_CREATE_UNINIT_EXT |
- EXT4_GET_BLOCKS_NO_NORMALIZE;
+ flags = EXT4_GET_BLOCKS_CREATE_UNINIT_EXT;
if (mode & FALLOC_FL_KEEP_SIZE)
flags |= EXT4_GET_BLOCKS_KEEP_SIZE;
+ /*
+ * Don't normalize the request if it can fit in one extent so
+ * that it doesn't get unnecessarily split into multiple
+ * extents.
+ */
+ if (len <= EXT_UNINIT_MAX_LEN << blkbits)
+ flags |= EXT4_GET_BLOCKS_NO_NORMALIZE;
retry:
while (ret >= 0 && ret < max_blocks) {
map.m_lblk = map.m_lblk + ret;
--
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