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

[Tyler Hicks]

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@xxxxxxxxxxxxxx>
> Signed-off-by: Yunchuan Wen <wenyunchuan@xxxxxxxxxxxxxx>
> Reviewed-by: Tyler Hicks <tyhicks@xxxxxxxxxxxxx>

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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