lkml.org 
[lkml]   [2007]   [May]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] zero_user_page uses in fs/buffer.c and fs/libfs.c
On Mon, 30 Apr 2007 00:04:31 -0700 (PDT)
Christoph Lameter <clameter@sgi.com> wrote:

>
> Replace open-coded kmap_atomic() and kunmap_atomic()
> surrounding two memory clear operations with zero_user_page(), as both
> memory operations act on the same page.
>
> Cc: Nate Diller <nate.diller@gmail.com>
> Signed-off-by: Christoph Lameter <clameter@sgi.com>
>
> ---
> fs/buffer.c | 29 ++++++++++-------------------
> fs/libfs.c | 10 +++++-----
> 2 files changed, 15 insertions(+), 24 deletions(-)
>
> Index: linux-2.6.21-rc7-mm2/fs/buffer.c
> ===================================================================
> --- linux-2.6.21-rc7-mm2.orig/fs/buffer.c 2007-04-27 22:51:27.000000000 -0700
> +++ linux-2.6.21-rc7-mm2/fs/buffer.c 2007-04-29 23:58:48.000000000 -0700
> @@ -1796,19 +1796,12 @@ static int __block_prepare_write(struct
> set_buffer_uptodate(bh);
> continue;
> }
> - if (block_end > to || block_start < from) {
> - void *kaddr;
> -
> - kaddr = kmap_atomic(page, KM_USER0);
> - if (block_end > to)
> - memset(kaddr+to, 0,
> - block_end-to);
> - if (block_start < from)
> - memset(kaddr+block_start,
> - 0, from-block_start);
> - flush_dcache_page(page);
> - kunmap_atomic(kaddr, KM_USER0);
> - }
> + if (block_end > to)
> + zero_user_page(page, to,
> + block_end - to, KM_USER0);
> + if (block_start < from)
> + zero_user_page(page, block_start,
> + from - block_start, KM_USER0);
> continue;
> }
> }
> @@ -2224,7 +2217,6 @@ int nobh_prepare_write(struct page *page
> unsigned block_in_page;
> unsigned block_start;
> sector_t block_in_file;
> - char *kaddr;
> int nr_reads = 0;
> int i;
> int ret = 0;
> @@ -2264,13 +2256,12 @@ int nobh_prepare_write(struct page *page
> if (PageUptodate(page))
> continue;
> if (buffer_new(&map_bh) || !buffer_mapped(&map_bh)) {
> - kaddr = kmap_atomic(page, KM_USER0);
> if (block_start < from)
> - memset(kaddr+block_start, 0, from-block_start);
> + zero_user_page(page, block_start,
> + from - block_start, KM_USER0);
> if (block_end > to)
> - memset(kaddr + to, 0, block_end - to);
> - flush_dcache_page(page);
> - kunmap_atomic(kaddr, KM_USER0);
> + zero_user_page(page, to,
> + block_end - to, KM_USER0);
> continue;
> }
> if (buffer_uptodate(&map_bh))
> Index: linux-2.6.21-rc7-mm2/fs/libfs.c
> ===================================================================
> --- linux-2.6.21-rc7-mm2.orig/fs/libfs.c 2007-04-27 22:51:27.000000000 -0700
> +++ linux-2.6.21-rc7-mm2/fs/libfs.c 2007-04-27 22:55:12.000000000 -0700
> @@ -338,11 +338,11 @@ int simple_prepare_write(struct file *fi
> {
> if (!PageUptodate(page)) {
> if (to - from != PAGE_CACHE_SIZE) {
> - void *kaddr = kmap_atomic(page, KM_USER0);
> - memset(kaddr, 0, from);
> - memset(kaddr + to, 0, PAGE_CACHE_SIZE - to);
> - flush_dcache_page(page);
> - kunmap_atomic(kaddr, KM_USER0);
> + if (from)
> + zero_user_page(page, 0, from, KM_USER0);
> + if (to < PAGE_CACHE_SIZE)
> + zero_user_page(page, to,
> + PAGE_CACHE_SIZE - to, KM_USER0);
> }
> }
> return 0;

As Satyam said, this will sometimes cause us to map and unmap the page
twice, and to run flush_dcache_page() twice. In not-terribly-uncommon
circumstances in very frequently called functions.

Doesn't seem worth it to me.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-05-02 02:29    [from the cache]
©2003-2011 Jasper Spaans