mm: buffered write cleanup

Quite a bit of code is used in maintaining these "cached pages" that are
probably pretty unlikely to get used. It would require a narrow race where
the page is inserted concurrently while this process is allocating a page
in order to create the spare page. Then a multi-page write into an uncached
part of the file, to make use of it.

Next, the buffered write path (and others) uses its own LRU pagevec when it
should be just using the per-CPU LRU pagevec (which will cut down on both data
and code size cacheline footprint). Also, these private LRU pagevecs are
emptied after just a very short time, in contrast with the per-CPU pagevecs
that are persistent. Net result: 7.3 times fewer lru_lock acquisitions required
to add the pages to pagecache for a bulk write (in 4K chunks).

[this gets rid of some cond_resched() calls in readahead.c and mpage.c due
 to clashes in -mm. What put them there, and why? ]

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 8 deletions

diff --git a/fs/mpage.c b/fs/mpage.c
index b1c3e5890508..d54f8f897224 100644
--- a/fs/mpage.c
+++ b/fs/mpage.c
@@ -379,31 +379,25 @@ mpage_readpages(struct address_space *mapping, struct list_head *pages,
         struct bio *bio = NULL;
         unsigned page_idx;
         sector_t last_block_in_bio = 0;
-        struct pagevec lru_pvec;
         struct buffer_head map_bh;
         unsigned long first_logical_block = 0;
 
         clear_buffer_mapped(&map_bh);
-        pagevec_init(&lru_pvec, 0);
         for (page_idx = 0; page_idx < nr_pages; page_idx++) {
                 struct page *page = list_entry(pages->prev, struct page, lru);
 
                 prefetchw(&page->flags);
                 list_del(&page->lru);
-                if (!add_to_page_cache(page, mapping,
+                if (!add_to_page_cache_lru(page, mapping,
                                         page->index, GFP_KERNEL)) {
                         bio = do_mpage_readpage(bio, page,
                                         nr_pages - page_idx,
                                         &last_block_in_bio, &map_bh,
                                         &first_logical_block,
                                         get_block);
-                        if (!pagevec_add(&lru_pvec, page))
-                                __pagevec_lru_add(&lru_pvec);
-                } else {
-                        page_cache_release(page);
                 }
+                page_cache_release(page);
         }
-        pagevec_lru_add(&lru_pvec);
         BUG_ON(!list_empty(pages));
         if (bio)
                 mpage_bio_submit(READ, bio);