ChangeSet 1.2231.1.149, 2005/03/28 19:57:54-08:00, [EMAIL PROTECTED]
[PATCH] pipe: save one pipe page
Save one page in pipe writev without incuring additional cost (just that
ampersand operator).
Signed-off-by: Prasanna Meda <[EMAIL PROTECTED]>
Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
pipe.c | 18 ++++++++++--------
1 files changed, 10 insertions(+), 8 deletions(-)
diff -Nru a/fs/pipe.c b/fs/pipe.c
--- a/fs/pipe.c 2005-03-28 21:39:15 -08:00
+++ b/fs/pipe.c 2005-03-28 21:39:15 -08:00
@@ -224,6 +224,7 @@
int do_wakeup;
struct iovec *iov = (struct iovec *)_iov;
size_t total_len;
+ ssize_t chars;
total_len = iov_length(iov, nr_segs);
/* Null write succeeds. */
@@ -242,24 +243,26 @@
}
/* We try to merge small writes */
- if (info->nrbufs && total_len < PAGE_SIZE) {
+ chars = total_len & (PAGE_SIZE-1); /* size of the last buffer */
+ if (info->nrbufs && chars != 0) {
int lastbuf = (info->curbuf + info->nrbufs - 1) &
(PIPE_BUFFERS-1);
struct pipe_buffer *buf = info->bufs + lastbuf;
struct pipe_buf_operations *ops = buf->ops;
int offset = buf->offset + buf->len;
- if (ops->can_merge && offset + total_len <= PAGE_SIZE) {
+ if (ops->can_merge && offset + chars <= PAGE_SIZE) {
void *addr = ops->map(filp, info, buf);
- int error = pipe_iov_copy_from_user(offset + addr, iov,
total_len);
+ int error = pipe_iov_copy_from_user(offset + addr, iov,
chars);
ops->unmap(info, buf);
ret = error;
do_wakeup = 1;
if (error)
goto out;
- buf->len += total_len;
- ret = total_len;
- goto out;
+ buf->len += chars;
+ total_len -= chars;
+ ret = chars;
+ if (!total_len)
+ goto out;
}
-
}
for (;;) {
@@ -271,7 +274,6 @@
}
bufs = info->nrbufs;
if (bufs < PIPE_BUFFERS) {
- ssize_t chars;
int newbuf = (info->curbuf + bufs) & (PIPE_BUFFERS-1);
struct pipe_buffer *buf = info->bufs + newbuf;
struct page *page = info->tmp_page;
-
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