| Message ID | 20181129164131.4716-1-nborisov@suse.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | btrfs: Refactor main loop in extent_readpages | expand |
On Thu, Nov 29, 2018 at 06:41:31PM +0200, Nikolay Borisov wrote: > extent_readpages processes all pages in the readlist in batches of 16, > this is implemented by a single for loop but thanks to an if condition > the loop does 2 things based on whether we've filled the batch or not. > Additionally due to the structure of the code there is an additional > check which deals with partial batches. > > Streamline all of this by explicitly using two loops. The outter one is > used to process all pages while the inner one just fills in the batch > of 16 (currently). Due to this new structure the code guarantees that > all pages are processed in the loop hence the code to deal with any > leftovers is eliminated. > > This also enable the compiler to inline __extent_readpages: > > ./scripts/bloat-o-meter fs/btrfs/extent_io.o extent_io.for > > add/remove: 0/1 grow/shrink: 1/0 up/down: 660/-820 (-160) > Function old new delta > extent_readpages 476 1136 +660 > __extent_readpages 820 - -820 > Total: Before=44315, After=44155, chg -0.36% > > Signed-off-by: Nikolay Borisov <nborisov@suse.com> > --- > fs/btrfs/extent_io.c | 37 ++++++++++++++++--------------------- > 1 file changed, 16 insertions(+), 21 deletions(-) > > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c > index 8332c5f4b1c3..233f835dd6f8 100644 > --- a/fs/btrfs/extent_io.c > +++ b/fs/btrfs/extent_io.c > @@ -4093,43 +4093,38 @@ int extent_writepages(struct address_space *mapping, > int extent_readpages(struct address_space *mapping, struct list_head *pages, > unsigned nr_pages) nr_pages becomes unused now. I've checked the MM code that calls here and it's guaranteed that the number of list 'pages' members is same as nr_pages. > { > +#define BTRFS_PAGES_BATCH 16 > + > struct bio *bio = NULL; > - unsigned page_idx; > unsigned long bio_flags = 0; > - struct page *pagepool[16]; > - struct page *page; > + struct page *pagepool[BTRFS_PAGES_BATCH]; I don't think we need the extra define, if struct page *pagepool[16]; ... for (nr = 0; nr < ARRAY_SIZE(pagepool) ... Otherwise ok, nice cleanup. Reviewed-by: David Sterba <dsterba@suse.com>
On 12.12.18 г. 16:40 ч., David Sterba wrote: > On Thu, Nov 29, 2018 at 06:41:31PM +0200, Nikolay Borisov wrote: >> extent_readpages processes all pages in the readlist in batches of 16, >> this is implemented by a single for loop but thanks to an if condition >> the loop does 2 things based on whether we've filled the batch or not. >> Additionally due to the structure of the code there is an additional >> check which deals with partial batches. >> >> Streamline all of this by explicitly using two loops. The outter one is >> used to process all pages while the inner one just fills in the batch >> of 16 (currently). Due to this new structure the code guarantees that >> all pages are processed in the loop hence the code to deal with any >> leftovers is eliminated. >> >> This also enable the compiler to inline __extent_readpages: >> >> ./scripts/bloat-o-meter fs/btrfs/extent_io.o extent_io.for >> >> add/remove: 0/1 grow/shrink: 1/0 up/down: 660/-820 (-160) >> Function old new delta >> extent_readpages 476 1136 +660 >> __extent_readpages 820 - -820 >> Total: Before=44315, After=44155, chg -0.36% >> >> Signed-off-by: Nikolay Borisov <nborisov@suse.com> >> --- >> fs/btrfs/extent_io.c | 37 ++++++++++++++++--------------------- >> 1 file changed, 16 insertions(+), 21 deletions(-) >> >> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c >> index 8332c5f4b1c3..233f835dd6f8 100644 >> --- a/fs/btrfs/extent_io.c >> +++ b/fs/btrfs/extent_io.c >> @@ -4093,43 +4093,38 @@ int extent_writepages(struct address_space *mapping, >> int extent_readpages(struct address_space *mapping, struct list_head *pages, >> unsigned nr_pages) > > nr_pages becomes unused now. I've checked the MM code that calls here > and it's guaranteed that the number of list 'pages' members is same as > nr_pages. Indeed, I missed that. > >> { >> +#define BTRFS_PAGES_BATCH 16 >> + >> struct bio *bio = NULL; >> - unsigned page_idx; >> unsigned long bio_flags = 0; >> - struct page *pagepool[16]; >> - struct page *page; >> + struct page *pagepool[BTRFS_PAGES_BATCH]; > > I don't think we need the extra define, if > > struct page *pagepool[16]; > > ... > > for (nr = 0; nr < ARRAY_SIZE(pagepool) ... > > Otherwise ok, nice cleanup. Fair enough, I'm ok with that as well. > > Reviewed-by: David Sterba <dsterba@suse.com> >
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 8332c5f4b1c3..233f835dd6f8 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -4093,43 +4093,38 @@ int extent_writepages(struct address_space *mapping, int extent_readpages(struct address_space *mapping, struct list_head *pages, unsigned nr_pages) { +#define BTRFS_PAGES_BATCH 16 + struct bio *bio = NULL; - unsigned page_idx; unsigned long bio_flags = 0; - struct page *pagepool[16]; - struct page *page; + struct page *pagepool[BTRFS_PAGES_BATCH]; struct extent_map *em_cached = NULL; struct extent_io_tree *tree = &BTRFS_I(mapping->host)->io_tree; int nr = 0; u64 prev_em_start = (u64)-1; - for (page_idx = 0; page_idx < nr_pages; page_idx++) { - page = lru_to_page(pages); + while (!list_empty(pages)) { + for (nr = 0; nr < BTRFS_PAGES_BATCH && !list_empty(pages);) { + struct page *page = lru_to_page(pages); - prefetchw(&page->flags); - list_del(&page->lru); - if (add_to_page_cache_lru(page, mapping, - page->index, - readahead_gfp_mask(mapping))) { - put_page(page); - continue; + prefetchw(&page->flags); + list_del(&page->lru); + if (add_to_page_cache_lru(page, mapping, page->index, + readahead_gfp_mask(mapping))) { + put_page(page); + continue; + } + + pagepool[nr++] = page; } - pagepool[nr++] = page; - if (nr < ARRAY_SIZE(pagepool)) - continue; __extent_readpages(tree, pagepool, nr, &em_cached, &bio, - &bio_flags, &prev_em_start); - nr = 0; + &bio_flags, &prev_em_start); } - if (nr) - __extent_readpages(tree, pagepool, nr, &em_cached, &bio, - &bio_flags, &prev_em_start); if (em_cached) free_extent_map(em_cached); - BUG_ON(!list_empty(pages)); if (bio) return submit_one_bio(bio, 0, bio_flags); return 0;
extent_readpages processes all pages in the readlist in batches of 16, this is implemented by a single for loop but thanks to an if condition the loop does 2 things based on whether we've filled the batch or not. Additionally due to the structure of the code there is an additional check which deals with partial batches. Streamline all of this by explicitly using two loops. The outter one is used to process all pages while the inner one just fills in the batch of 16 (currently). Due to this new structure the code guarantees that all pages are processed in the loop hence the code to deal with any leftovers is eliminated. This also enable the compiler to inline __extent_readpages: ./scripts/bloat-o-meter fs/btrfs/extent_io.o extent_io.for add/remove: 0/1 grow/shrink: 1/0 up/down: 660/-820 (-160) Function old new delta extent_readpages 476 1136 +660 __extent_readpages 820 - -820 Total: Before=44315, After=44155, chg -0.36% Signed-off-by: Nikolay Borisov <nborisov@suse.com> --- fs/btrfs/extent_io.c | 37 ++++++++++++++++--------------------- 1 file changed, 16 insertions(+), 21 deletions(-)