readahead: move synchronous readahead call out of splice loop (431a4820) · Commits · 戴 / test

Move synchronous page_cache_readahead_ondemand() call out of splice loop. This avoids one pointless page allocation/insertion in case of non-zero ra_pages, or many pointless readahead calls in case of zero ra_pages. Note that if a user sets ra_pages to less than PIPE_BUFFERS=16 pages, he will not get expected readahead behavior anyway. The splice code works in batches of 16 pages, which can be taken as another form of synchronous readahead. Signed-off-by:

Fengguang Wu <wfg@mail.ustc.edu.cn> Cc: Jens Axboe <jens.axboe@oracle.com> Cc: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

fs/splice.c

+6 −5

Original line number	Diff line number	Diff line
		@@ -290,13 +290,17 @@ __generic_file_splice_read(struct file in, loff_t ppos,
		* Lookup the (hopefully) full range of pages we need.
		*/
		spd.nr_pages = find_get_pages_contig(mapping, index, nr_pages, pages);
		index += spd.nr_pages;

		/*
		* If find_get_pages_contig() returned fewer pages than we needed,
		* allocate the rest and fill in the holes.
		* readahead/allocate the rest and fill in the holes.
		*/
		if (spd.nr_pages < nr_pages)
		page_cache_readahead_ondemand(mapping, &in->f_ra, in,
		NULL, index, nr_pages - spd.nr_pages);

		error = 0;
		index += spd.nr_pages;
		while (spd.nr_pages < nr_pages) {
		/*
		* Page could be there, find_get_pages_contig() breaks on
		@@ -304,9 +308,6 @@ __generic_file_splice_read(struct file in, loff_t ppos,
		*/
		page = find_get_page(mapping, index);
		if (!page) {
		page_cache_readahead_ondemand(mapping, &in->f_ra, in,
		NULL, index, nr_pages - spd.nr_pages);

		/*
		* page didn't exist, allocate one.
		*/

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