From: Fengguang Wu Date: Thu, 19 Jul 2007 08:48:06 +0000 (-0700) Subject: readahead: pass real splice size X-Git-Tag: v2.6.23-rc1~428 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d8983910a4045fa21022cfccf76ed13eb40fd7f5;p=linux-2.6 readahead: pass real splice size Pass real splice size to page_cache_readahead_ondemand(). The splice code works in chunks of 16 pages internally. The readahead code should be told of the overall splice size, instead of the internal chunk size. Otherwize bad things may happen. Imagine some 17-page random splice reads. The code before this patch will result in two readahead calls: readahead(16); readahead(1); That leads to one 16-page I/O and one 32-page I/O: one extra I/O and 31 readahead miss pages. Signed-off-by: Fengguang Wu Cc: Jens Axboe Cc: Rusty Russell Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/fs/splice.c b/fs/splice.c index 421b3b8211..6ddd0329f8 100644 --- a/fs/splice.c +++ b/fs/splice.c @@ -265,7 +265,7 @@ __generic_file_splice_read(struct file *in, loff_t *ppos, unsigned int flags) { struct address_space *mapping = in->f_mapping; - unsigned int loff, nr_pages; + unsigned int loff, nr_pages, req_pages; struct page *pages[PIPE_BUFFERS]; struct partial_page partial[PIPE_BUFFERS]; struct page *page; @@ -281,10 +281,8 @@ __generic_file_splice_read(struct file *in, loff_t *ppos, index = *ppos >> PAGE_CACHE_SHIFT; loff = *ppos & ~PAGE_CACHE_MASK; - nr_pages = (len + loff + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT; - - if (nr_pages > PIPE_BUFFERS) - nr_pages = PIPE_BUFFERS; + req_pages = (len + loff + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT; + nr_pages = min(req_pages, (unsigned)PIPE_BUFFERS); /* * Lookup the (hopefully) full range of pages we need. @@ -298,7 +296,7 @@ __generic_file_splice_read(struct file *in, loff_t *ppos, */ if (spd.nr_pages < nr_pages) page_cache_readahead_ondemand(mapping, &in->f_ra, in, - NULL, index, nr_pages - spd.nr_pages); + NULL, index, req_pages - spd.nr_pages); error = 0; while (spd.nr_pages < nr_pages) { @@ -355,7 +353,7 @@ __generic_file_splice_read(struct file *in, loff_t *ppos, if (PageReadahead(page)) page_cache_readahead_ondemand(mapping, &in->f_ra, in, - page, index, nr_pages - page_nr); + page, index, req_pages - page_nr); /* * If the page isn't uptodate, we may need to start io on it