[PATCH] eCryptfs: Avoid unnecessary disk read and data decryption during writing

[PATCH] eCryptfs: Avoid unnecessary disk read and data decryption during writing

[Li Wang]

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>
Reviewed-by: Tyler Hicks <tyhicks@canonical.com>
---
 fs/ecryptfs/mmap.c |   12 ++++++++++--
 1 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/fs/ecryptfs/mmap.c b/fs/ecryptfs/mmap.c
index bd1d57f..564a1fa 100644
--- a/fs/ecryptfs/mmap.c
+++ b/fs/ecryptfs/mmap.c
@@ -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) {
-- 
1.7.6.5

Re: [PATCH] eCryptfs: Avoid unnecessary disk read and data decryption during writing

[Tyler Hicks]

[-- Attachment #1: Type: text/plain, Size: 2687 bytes --]

On 2012-10-30 19:52:40, Li Wang wrote:
> 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>
> Reviewed-by: Tyler Hicks <tyhicks@canonical.com>

Thanks again, Li. I've pushed this to my next branch.

I lost track of it last time. Sorry about that!

Tyler

> ---
>  fs/ecryptfs/mmap.c |   12 ++++++++++--
>  1 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ecryptfs/mmap.c b/fs/ecryptfs/mmap.c
> index bd1d57f..564a1fa 100644
> --- a/fs/ecryptfs/mmap.c
> +++ b/fs/ecryptfs/mmap.c
> @@ -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) {
> -- 
> 1.7.6.5
> 
> --
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