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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>
This commit is contained in:
Li Wang 2012-10-30 19:52:40 +08:00 committed by Tyler Hicks
parent 0e4a43ed08
commit e4bc6522d5
1 changed files with 10 additions and 2 deletions
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12
fs/ecryptfs/mmap.c
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@ -338,7 +338,8 @@ static int ecryptfs_write_begin(struct file *file,
if (prev_page_end_size
>= i_size_read(page->mapping->host)) {
zero_user(page, 0, PAGE_CACHE_SIZE);
} else {
SetPageUptodate(page);
} else if (len < PAGE_CACHE_SIZE) {
rc = ecryptfs_decrypt_page(page);
if (rc) {
printk(KERN_ERR "%s: Error decrypting "
@ -348,8 +349,8 @@ static int ecryptfs_write_begin(struct file *file,
ClearPageUptodate(page);
goto out;
}
SetPageUptodate(page);
}
SetPageUptodate(page);
}
}
/* If creating a page or more of holes, zero them out via truncate.
@ -499,6 +500,13 @@ static int ecryptfs_write_end(struct file *file,
}
goto out;
}
if (!PageUptodate(page)) {
if (copied < PAGE_CACHE_SIZE) {
rc = 0;
goto out;
}
SetPageUptodate(page);
}
/* Fills in zeros if 'to' goes beyond inode size */
rc = fill_zeros_to_end_of_page(page, to);
if (rc) {