Matthew Wilcox
2020-Feb-19 21:00 UTC
[Ocfs2-devel] [PATCH v7 09/24] mm: Put readahead pages in cache earlier
From: "Matthew Wilcox (Oracle)" <willy at infradead.org> When populating the page cache for readahead, mappings that use ->readpages must populate the page cache themselves as the pages are passed on a linked list which would normally be used for the page cache's LRU. For mappings that use ->readpage or the upcoming ->readahead method, we can put the pages into the page cache as soon as they're allocated, which solves a race between readahead and direct IO. It also lets us remove the gfp argument from read_pages(). Use the new readahead_page() API to implement the repeated calls to ->readpage(), just like most filesystems will. This iterator also supports huge pages, even though none of the filesystems have been converted to use them yet. Signed-off-by: Matthew Wilcox (Oracle) <willy at infradead.org> --- include/linux/pagemap.h | 20 +++++++++++++++++ mm/readahead.c | 48 +++++++++++++++++++++++++---------------- 2 files changed, 49 insertions(+), 19 deletions(-) diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index 55fcea0249e6..4989d330fada 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -647,8 +647,28 @@ struct readahead_control { /* private: use the readahead_* accessors instead */ pgoff_t _index; unsigned int _nr_pages; + unsigned int _batch_count; }; +static inline struct page *readahead_page(struct readahead_control *rac) +{ + struct page *page; + + BUG_ON(rac->_batch_count > rac->_nr_pages); + rac->_nr_pages -= rac->_batch_count; + rac->_index += rac->_batch_count; + rac->_batch_count = 0; + + if (!rac->_nr_pages) + return NULL; + + page = xa_load(&rac->mapping->i_pages, rac->_index); + VM_BUG_ON_PAGE(!PageLocked(page), page); + rac->_batch_count = hpage_nr_pages(page); + + return page; +} + /* The number of pages in this readahead block */ static inline unsigned int readahead_count(struct readahead_control *rac) { diff --git a/mm/readahead.c b/mm/readahead.c index 83df5c061d33..aaa209559ba2 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -113,15 +113,14 @@ int read_cache_pages(struct address_space *mapping, struct list_head *pages, EXPORT_SYMBOL(read_cache_pages); -static void read_pages(struct readahead_control *rac, struct list_head *pages, - gfp_t gfp) +static void read_pages(struct readahead_control *rac, struct list_head *pages) { const struct address_space_operations *aops = rac->mapping->a_ops; + struct page *page; struct blk_plug plug; - unsigned page_idx; if (!readahead_count(rac)) - return; + goto out; blk_start_plug(&plug); @@ -130,23 +129,23 @@ static void read_pages(struct readahead_control *rac, struct list_head *pages, readahead_count(rac)); /* Clean up the remaining pages */ put_pages_list(pages); - goto out; - } - - for (page_idx = 0; page_idx < readahead_count(rac); page_idx++) { - struct page *page = lru_to_page(pages); - list_del(&page->lru); - if (!add_to_page_cache_lru(page, rac->mapping, page->index, - gfp)) + rac->_index += rac->_nr_pages; + rac->_nr_pages = 0; + } else { + while ((page = readahead_page(rac))) { aops->readpage(rac->file, page); - put_page(page); + put_page(page); + } } -out: blk_finish_plug(&plug); BUG_ON(!list_empty(pages)); - rac->_nr_pages = 0; + BUG_ON(readahead_count(rac)); + +out: + /* If we were called due to a conflicting page, skip over it */ + rac->_index++; } /* @@ -165,9 +164,11 @@ void __do_page_cache_readahead(struct address_space *mapping, LIST_HEAD(page_pool); loff_t isize = i_size_read(inode); gfp_t gfp_mask = readahead_gfp_mask(mapping); + bool use_list = mapping->a_ops->readpages; struct readahead_control rac = { .mapping = mapping, .file = filp, + ._index = index, ._nr_pages = 0, }; unsigned long i; @@ -184,6 +185,8 @@ void __do_page_cache_readahead(struct address_space *mapping, if (index + i > end_index) break; + BUG_ON(index + i != rac._index + rac._nr_pages); + page = xa_load(&mapping->i_pages, index + i); if (page && !xa_is_value(page)) { /* @@ -191,15 +194,22 @@ void __do_page_cache_readahead(struct address_space *mapping, * contiguous pages before continuing with the next * batch. */ - read_pages(&rac, &page_pool, gfp_mask); + read_pages(&rac, &page_pool); continue; } page = __page_cache_alloc(gfp_mask); if (!page) break; - page->index = index + i; - list_add(&page->lru, &page_pool); + if (use_list) { + page->index = index + i; + list_add(&page->lru, &page_pool); + } else if (add_to_page_cache_lru(page, mapping, index + i, + gfp_mask) < 0) { + put_page(page); + read_pages(&rac, &page_pool); + continue; + } if (i == nr_to_read - lookahead_size) SetPageReadahead(page); rac._nr_pages++; @@ -210,7 +220,7 @@ void __do_page_cache_readahead(struct address_space *mapping, * uptodate then the caller will launch readpage again, and * will then handle the error. */ - read_pages(&rac, &page_pool, gfp_mask); + read_pages(&rac, &page_pool); } /* -- 2.25.0
John Hubbard
2020-Feb-21 03:19 UTC
[Ocfs2-devel] [PATCH v7 09/24] mm: Put readahead pages in cache earlier
On 2/19/20 1:00 PM, Matthew Wilcox wrote:> From: "Matthew Wilcox (Oracle)" <willy at infradead.org> > > When populating the page cache for readahead, mappings that use > ->readpages must populate the page cache themselves as the pages are > passed on a linked list which would normally be used for the page cache's > LRU. For mappings that use ->readpage or the upcoming ->readahead method, > we can put the pages into the page cache as soon as they're allocated, > which solves a race between readahead and direct IO. It also lets us > remove the gfp argument from read_pages(). > > Use the new readahead_page() API to implement the repeated calls to > ->readpage(), just like most filesystems will. This iterator also > supports huge pages, even though none of the filesystems have been > converted to use them yet. > > Signed-off-by: Matthew Wilcox (Oracle) <willy at infradead.org> > --- > include/linux/pagemap.h | 20 +++++++++++++++++ > mm/readahead.c | 48 +++++++++++++++++++++++++---------------- > 2 files changed, 49 insertions(+), 19 deletions(-) > > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h > index 55fcea0249e6..4989d330fada 100644 > --- a/include/linux/pagemap.h > +++ b/include/linux/pagemap.h > @@ -647,8 +647,28 @@ struct readahead_control { > /* private: use the readahead_* accessors instead */ > pgoff_t _index; > unsigned int _nr_pages; > + unsigned int _batch_count; > }; > > +static inline struct page *readahead_page(struct readahead_control *rac) > +{ > + struct page *page; > + > + BUG_ON(rac->_batch_count > rac->_nr_pages); > + rac->_nr_pages -= rac->_batch_count; > + rac->_index += rac->_batch_count; > + rac->_batch_count = 0;Is it intentional, to set rac->_batch_count twice (here, and below)? The only reason I can see is if a caller needs to use ->_batch_count in the "return NULL" case, which doesn't seem to come up...> + > + if (!rac->_nr_pages) > + return NULL; > + > + page = xa_load(&rac->mapping->i_pages, rac->_index); > + VM_BUG_ON_PAGE(!PageLocked(page), page); > + rac->_batch_count = hpage_nr_pages(page); > + > + return page; > +} > + > /* The number of pages in this readahead block */ > static inline unsigned int readahead_count(struct readahead_control *rac) > { > diff --git a/mm/readahead.c b/mm/readahead.c > index 83df5c061d33..aaa209559ba2 100644 > --- a/mm/readahead.c > +++ b/mm/readahead.c > @@ -113,15 +113,14 @@ int read_cache_pages(struct address_space *mapping, struct list_head *pages, > > EXPORT_SYMBOL(read_cache_pages); > > -static void read_pages(struct readahead_control *rac, struct list_head *pages, > - gfp_t gfp) > +static void read_pages(struct readahead_control *rac, struct list_head *pages) > { > const struct address_space_operations *aops = rac->mapping->a_ops; > + struct page *page; > struct blk_plug plug; > - unsigned page_idx; > > if (!readahead_count(rac)) > - return; > + goto out; > > blk_start_plug(&plug); > > @@ -130,23 +129,23 @@ static void read_pages(struct readahead_control *rac, struct list_head *pages, > readahead_count(rac)); > /* Clean up the remaining pages */ > put_pages_list(pages); > - goto out; > - } > - > - for (page_idx = 0; page_idx < readahead_count(rac); page_idx++) { > - struct page *page = lru_to_page(pages); > - list_del(&page->lru); > - if (!add_to_page_cache_lru(page, rac->mapping, page->index, > - gfp)) > + rac->_index += rac->_nr_pages; > + rac->_nr_pages = 0; > + } else { > + while ((page = readahead_page(rac))) { > aops->readpage(rac->file, page); > - put_page(page); > + put_page(page); > + } > } > > -out: > blk_finish_plug(&plug); > > BUG_ON(!list_empty(pages)); > - rac->_nr_pages = 0; > + BUG_ON(readahead_count(rac)); > + > +out: > + /* If we were called due to a conflicting page, skip over it */Tiny documentation nit: What if we were *not* called due to a conflicting page? (And what is a "conflicting page", in this context, btw?) The next line unconditionally moves the index ahead, so the "if" part of the comment really confuses me.> + rac->_index++; > } > > /* > @@ -165,9 +164,11 @@ void __do_page_cache_readahead(struct address_space *mapping, > LIST_HEAD(page_pool); > loff_t isize = i_size_read(inode); > gfp_t gfp_mask = readahead_gfp_mask(mapping); > + bool use_list = mapping->a_ops->readpages; > struct readahead_control rac = { > .mapping = mapping, > .file = filp, > + ._index = index, > ._nr_pages = 0, > }; > unsigned long i; > @@ -184,6 +185,8 @@ void __do_page_cache_readahead(struct address_space *mapping, > if (index + i > end_index) > break; > > + BUG_ON(index + i != rac._index + rac._nr_pages); > + > page = xa_load(&mapping->i_pages, index + i); > if (page && !xa_is_value(page)) { > /* > @@ -191,15 +194,22 @@ void __do_page_cache_readahead(struct address_space *mapping, > * contiguous pages before continuing with the next > * batch. > */ > - read_pages(&rac, &page_pool, gfp_mask); > + read_pages(&rac, &page_pool); > continue; > } > > page = __page_cache_alloc(gfp_mask); > if (!page) > break; > - page->index = index + i; > - list_add(&page->lru, &page_pool); > + if (use_list) { > + page->index = index + i; > + list_add(&page->lru, &page_pool); > + } else if (add_to_page_cache_lru(page, mapping, index + i, > + gfp_mask) < 0) {I still think you'll want to compare against !=0, rather than < 0, here.> + put_page(page); > + read_pages(&rac, &page_pool);Doing a read_pages() in the error case is because...actually, I'm not sure yet. Why do we do this? Effectively it's a retry?> + continue; > + } > if (i == nr_to_read - lookahead_size) > SetPageReadahead(page); > rac._nr_pages++; > @@ -210,7 +220,7 @@ void __do_page_cache_readahead(struct address_space *mapping, > * uptodate then the caller will launch readpage again, and > * will then handle the error. > */ > - read_pages(&rac, &page_pool, gfp_mask); > + read_pages(&rac, &page_pool); > } > > /* >Didn't spot any actual errors, just mainly my own questions here. :) thanks, -- John Hubbard NVIDIA
Christoph Hellwig
2020-Feb-24 21:40 UTC
[Ocfs2-devel] [PATCH v7 09/24] mm: Put readahead pages in cache earlier
On Wed, Feb 19, 2020 at 01:00:48PM -0800, Matthew Wilcox wrote:> From: "Matthew Wilcox (Oracle)" <willy at infradead.org> > > When populating the page cache for readahead, mappings that use > ->readpages must populate the page cache themselves as the pages are > passed on a linked list which would normally be used for the page cache's > LRU. For mappings that use ->readpage or the upcoming ->readahead method, > we can put the pages into the page cache as soon as they're allocated, > which solves a race between readahead and direct IO. It also lets us > remove the gfp argument from read_pages(). > > Use the new readahead_page() API to implement the repeated calls to > ->readpage(), just like most filesystems will. This iterator also > supports huge pages, even though none of the filesystems have been > converted to use them yet. > > Signed-off-by: Matthew Wilcox (Oracle) <willy at infradead.org> > --- > include/linux/pagemap.h | 20 +++++++++++++++++ > mm/readahead.c | 48 +++++++++++++++++++++++++---------------- > 2 files changed, 49 insertions(+), 19 deletions(-) > > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h > index 55fcea0249e6..4989d330fada 100644 > --- a/include/linux/pagemap.h > +++ b/include/linux/pagemap.h > @@ -647,8 +647,28 @@ struct readahead_control { > /* private: use the readahead_* accessors instead */ > pgoff_t _index; > unsigned int _nr_pages; > + unsigned int _batch_count; > }; > > +static inline struct page *readahead_page(struct readahead_control *rac) > +{ > + struct page *page; > + > + BUG_ON(rac->_batch_count > rac->_nr_pages); > + rac->_nr_pages -= rac->_batch_count; > + rac->_index += rac->_batch_count; > + rac->_batch_count = 0; > + > + if (!rac->_nr_pages) > + return NULL; > + > + page = xa_load(&rac->mapping->i_pages, rac->_index); > + VM_BUG_ON_PAGE(!PageLocked(page), page); > + rac->_batch_count = hpage_nr_pages(page); > + > + return page; > +} > + > /* The number of pages in this readahead block */ > static inline unsigned int readahead_count(struct readahead_control *rac) > { > diff --git a/mm/readahead.c b/mm/readahead.c > index 83df5c061d33..aaa209559ba2 100644 > --- a/mm/readahead.c > +++ b/mm/readahead.c > @@ -113,15 +113,14 @@ int read_cache_pages(struct address_space *mapping, struct list_head *pages, > > EXPORT_SYMBOL(read_cache_pages); > > -static void read_pages(struct readahead_control *rac, struct list_head *pages, > - gfp_t gfp) > +static void read_pages(struct readahead_control *rac, struct list_head *pages) > { > const struct address_space_operations *aops = rac->mapping->a_ops; > + struct page *page; > struct blk_plug plug; > - unsigned page_idx; > > if (!readahead_count(rac)) > - return; > + goto out; > > blk_start_plug(&plug); > > @@ -130,23 +129,23 @@ static void read_pages(struct readahead_control *rac, struct list_head *pages, > readahead_count(rac)); > /* Clean up the remaining pages */ > put_pages_list(pages); > - goto out; > - } > - > - for (page_idx = 0; page_idx < readahead_count(rac); page_idx++) { > - struct page *page = lru_to_page(pages); > - list_del(&page->lru); > - if (!add_to_page_cache_lru(page, rac->mapping, page->index, > - gfp)) > + rac->_index += rac->_nr_pages; > + rac->_nr_pages = 0; > + } else { > + while ((page = readahead_page(rac))) { > aops->readpage(rac->file, page); > - put_page(page); > + put_page(page); > + } > } > > -out: > blk_finish_plug(&plug); > > BUG_ON(!list_empty(pages)); > - rac->_nr_pages = 0; > + BUG_ON(readahead_count(rac)); > + > +out: > + /* If we were called due to a conflicting page, skip over it */ > + rac->_index++; > } > > /* > @@ -165,9 +164,11 @@ void __do_page_cache_readahead(struct address_space *mapping, > LIST_HEAD(page_pool); > loff_t isize = i_size_read(inode); > gfp_t gfp_mask = readahead_gfp_mask(mapping); > + bool use_list = mapping->a_ops->readpages;I find this single use variable a little weird. Not a dealbreaker, but just checking the methods would seem a little more obvious to me. Except for this and the other nitpick the patch looks good to me: Reviewed-by: Christoph Hellwig <hch at lst.de>