eCryptfs: Avoid unnecessary disk read and data decryption during writing
authorLi Wang <wangli@kylinos.com.cn>
Tue, 30 Oct 2012 11:52:40 +0000 (19:52 +0800)
committerTyler Hicks <tyhicks@canonical.com>
Thu, 8 Nov 2012 01:56:16 +0000 (17:56 -0800)
commite4bc6522d53b7b8eb02cfac35fd18275fd86269d
tree9b426d57ab9a433422debaf44ae7dad498acc15e
parent0e4a43ed08e2f44aa7b96aa95d0a540d675483e1
eCryptfs: Avoid unnecessary disk read and data decryption during writing

ecryptfs_write_begin grabs a page from page cache for writing.
If the page contains invalid data, or data older than the
counterpart on the disk, eCryptfs will read out the
corresponing data from the disk into the page, decrypt them,
then perform writing. However, for this page, if the length
of the data to be written into is equal to page size,
that means the whole page of data will be overwritten,
in which case, it does not matter whatever the data were before,
it is beneficial to perform writing directly rather than bothering
to read and decrypt first.

With this optimization, according to our test on a machine with
Intel Core 2 Duo processor, iozone 'write' operation on an existing
file with write size being multiple of page size will enjoy a steady
3x speedup.

Signed-off-by: Li Wang <wangli@kylinos.com.cn>
Signed-off-by: Yunchuan Wen <wenyunchuan@kylinos.com.cn>
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
fs/ecryptfs/mmap.c