| Message ID | 20200219210103.32400-11-willy@infradead.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Change readahead API | expand |
On 19 Feb 2020, at 16:00, Matthew Wilcox wrote: > From: "Matthew Wilcox (Oracle)" <willy@infradead.org> > > This replaces ->readpages with a saner interface: > - Return void instead of an ignored error code. > - Page cache is already populated with locked pages when ->readahead > is called. > - New arguments can be passed to the implementation without changing > all the filesystems that use a common helper function like > mpage_readahead(). > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> > --- > Documentation/filesystems/locking.rst | 6 +++++- > Documentation/filesystems/vfs.rst | 15 +++++++++++++++ > include/linux/fs.h | 2 ++ > include/linux/pagemap.h | 18 ++++++++++++++++++ > mm/readahead.c | 12 ++++++++++-- > 5 files changed, 50 insertions(+), 3 deletions(-) > > diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst > index 5057e4d9dcd1..0af2e0e11461 100644 > --- a/Documentation/filesystems/locking.rst > +++ b/Documentation/filesystems/locking.rst > @@ -239,6 +239,7 @@ prototypes:: > int (*readpage)(struct file *, struct page *); > int (*writepages)(struct address_space *, struct writeback_control *); > int (*set_page_dirty)(struct page *page); > + void (*readahead)(struct readahead_control *); > int (*readpages)(struct file *filp, struct address_space *mapping, > struct list_head *pages, unsigned nr_pages); > int (*write_begin)(struct file *, struct address_space *mapping, > @@ -271,7 +272,8 @@ writepage: yes, unlocks (see below) > readpage: yes, unlocks > writepages: > set_page_dirty no > -readpages: > +readahead: yes, unlocks > +readpages: no > write_begin: locks the page exclusive > write_end: yes, unlocks exclusive > bmap: > @@ -295,6 +297,8 @@ the request handler (/dev/loop). > ->readpage() unlocks the page, either synchronously or via I/O > completion. > > +->readahead() unlocks the pages that I/O is attempted on like ->readpage(). > + > ->readpages() populates the pagecache with the passed pages and starts > I/O against them. They come unlocked upon I/O completion. > > diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst > index 7d4d09dd5e6d..ed17771c212b 100644 > --- a/Documentation/filesystems/vfs.rst > +++ b/Documentation/filesystems/vfs.rst > @@ -706,6 +706,7 @@ cache in your filesystem. The following members are defined: > int (*readpage)(struct file *, struct page *); > int (*writepages)(struct address_space *, struct writeback_control *); > int (*set_page_dirty)(struct page *page); > + void (*readahead)(struct readahead_control *); > int (*readpages)(struct file *filp, struct address_space *mapping, > struct list_head *pages, unsigned nr_pages); > int (*write_begin)(struct file *, struct address_space *mapping, > @@ -781,12 +782,26 @@ cache in your filesystem. The following members are defined: > If defined, it should set the PageDirty flag, and the > PAGECACHE_TAG_DIRTY tag in the radix tree. > > +``readahead`` > + Called by the VM to read pages associated with the address_space > + object. The pages are consecutive in the page cache and are > + locked. The implementation should decrement the page refcount > + after starting I/O on each page. Usually the page will be > + unlocked by the I/O completion handler. If the filesystem decides > + to stop attempting I/O before reaching the end of the readahead > + window, it can simply return. The caller will decrement the page > + refcount and unlock the remaining pages for you. Set PageUptodate > + if the I/O completes successfully. Setting PageError on any page > + will be ignored; simply unlock the page if an I/O error occurs. > + > ``readpages`` > called by the VM to read pages associated with the address_space > object. This is essentially just a vector version of readpage. > Instead of just one page, several pages are requested. > readpages is only used for read-ahead, so read errors are > ignored. If anything goes wrong, feel free to give up. > + This interface is deprecated and will be removed by the end of > + 2020; implement readahead instead. > > ``write_begin`` > Called by the generic buffered write code to ask the filesystem > diff --git a/include/linux/fs.h b/include/linux/fs.h > index 3cd4fe6b845e..d4e2d2964346 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -292,6 +292,7 @@ enum positive_aop_returns { > struct page; > struct address_space; > struct writeback_control; > +struct readahead_control; > > /* > * Write life time hint values. > @@ -375,6 +376,7 @@ struct address_space_operations { > */ > int (*readpages)(struct file *filp, struct address_space *mapping, > struct list_head *pages, unsigned nr_pages); > + void (*readahead)(struct readahead_control *); > > int (*write_begin)(struct file *, struct address_space *mapping, > loff_t pos, unsigned len, unsigned flags, > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h > index 4989d330fada..b3008605fd1b 100644 > --- a/include/linux/pagemap.h > +++ b/include/linux/pagemap.h > @@ -669,6 +669,24 @@ static inline struct page *readahead_page(struct readahead_control *rac) > return page; > } > > +/* The byte offset into the file of this readahead block */ > +static inline loff_t readahead_pos(struct readahead_control *rac) > +{ > + return (loff_t)rac->_index * PAGE_SIZE; > +} > + > +/* The number of bytes in this readahead block */ > +static inline loff_t readahead_length(struct readahead_control *rac) > +{ > + return (loff_t)rac->_nr_pages * PAGE_SIZE; > +} > + > +/* The index of the first page in this readahead block */ > +static inline unsigned int readahead_index(struct readahead_control *rac) > +{ > + return rac->_index; > +} rac->_index is pgoff_t, so readahead_index() should return the same type, right? BTW, pgoff_t is unsigned long. > + > /* 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 aaa209559ba2..07cdfbf00f4b 100644 > --- a/mm/readahead.c > +++ b/mm/readahead.c > @@ -124,7 +124,14 @@ static void read_pages(struct readahead_control *rac, struct list_head *pages) > > blk_start_plug(&plug); > > - if (aops->readpages) { > + if (aops->readahead) { > + aops->readahead(rac); > + /* Clean up the remaining pages */ > + while ((page = readahead_page(rac))) { > + unlock_page(page); > + put_page(page); > + } > + } else if (aops->readpages) { > aops->readpages(rac->file, rac->mapping, pages, > readahead_count(rac)); > /* Clean up the remaining pages */ > @@ -234,7 +241,8 @@ void force_page_cache_readahead(struct address_space *mapping, > struct file_ra_state *ra = &filp->f_ra; > unsigned long max_pages; > > - if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages)) > + if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages && > + !mapping->a_ops->readahead)) > return; > > /* > -- > 2.25.0 -- Best Regards, Yan Zi
On Thu, Feb 20, 2020 at 10:00:30AM -0500, Zi Yan wrote: > > +/* The index of the first page in this readahead block */ > > +static inline unsigned int readahead_index(struct readahead_control *rac) > > +{ > > + return rac->_index; > > +} > > rac->_index is pgoff_t, so readahead_index() should return the same type, right? > BTW, pgoff_t is unsigned long. Oh my goodness! Thank you for spotting that. Fortunately, it's only currently used by tracepoints, so it wasn't causing any trouble, but that's a nasty landmine to leave lying around. Fixed: static inline pgoff_t readahead_index(struct readahead_control *rac)
On 2/19/20 1:00 PM, Matthew Wilcox wrote: > From: "Matthew Wilcox (Oracle)" <willy@infradead.org> > > This replaces ->readpages with a saner interface: > - Return void instead of an ignored error code. > - Page cache is already populated with locked pages when ->readahead > is called. > - New arguments can be passed to the implementation without changing > all the filesystems that use a common helper function like > mpage_readahead(). > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> > --- > Documentation/filesystems/locking.rst | 6 +++++- > Documentation/filesystems/vfs.rst | 15 +++++++++++++++ > include/linux/fs.h | 2 ++ > include/linux/pagemap.h | 18 ++++++++++++++++++ > mm/readahead.c | 12 ++++++++++-- > 5 files changed, 50 insertions(+), 3 deletions(-) This all looks correct to me, so: Reviewed-by: John Hubbard <jhubbard@nvidia.com> thanks,
Looks fine modulo the little data type issue:
Reviewed-by: Christoph Hellwig <hch@lst.de>
diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst index 5057e4d9dcd1..0af2e0e11461 100644 --- a/Documentation/filesystems/locking.rst +++ b/Documentation/filesystems/locking.rst @@ -239,6 +239,7 @@ prototypes:: int (*readpage)(struct file *, struct page *); int (*writepages)(struct address_space *, struct writeback_control *); int (*set_page_dirty)(struct page *page); + void (*readahead)(struct readahead_control *); int (*readpages)(struct file *filp, struct address_space *mapping, struct list_head *pages, unsigned nr_pages); int (*write_begin)(struct file *, struct address_space *mapping, @@ -271,7 +272,8 @@ writepage: yes, unlocks (see below) readpage: yes, unlocks writepages: set_page_dirty no -readpages: +readahead: yes, unlocks +readpages: no write_begin: locks the page exclusive write_end: yes, unlocks exclusive bmap: @@ -295,6 +297,8 @@ the request handler (/dev/loop). ->readpage() unlocks the page, either synchronously or via I/O completion. +->readahead() unlocks the pages that I/O is attempted on like ->readpage(). + ->readpages() populates the pagecache with the passed pages and starts I/O against them. They come unlocked upon I/O completion. diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst index 7d4d09dd5e6d..ed17771c212b 100644 --- a/Documentation/filesystems/vfs.rst +++ b/Documentation/filesystems/vfs.rst @@ -706,6 +706,7 @@ cache in your filesystem. The following members are defined: int (*readpage)(struct file *, struct page *); int (*writepages)(struct address_space *, struct writeback_control *); int (*set_page_dirty)(struct page *page); + void (*readahead)(struct readahead_control *); int (*readpages)(struct file *filp, struct address_space *mapping, struct list_head *pages, unsigned nr_pages); int (*write_begin)(struct file *, struct address_space *mapping, @@ -781,12 +782,26 @@ cache in your filesystem. The following members are defined: If defined, it should set the PageDirty flag, and the PAGECACHE_TAG_DIRTY tag in the radix tree. +``readahead`` + Called by the VM to read pages associated with the address_space + object. The pages are consecutive in the page cache and are + locked. The implementation should decrement the page refcount + after starting I/O on each page. Usually the page will be + unlocked by the I/O completion handler. If the filesystem decides + to stop attempting I/O before reaching the end of the readahead + window, it can simply return. The caller will decrement the page + refcount and unlock the remaining pages for you. Set PageUptodate + if the I/O completes successfully. Setting PageError on any page + will be ignored; simply unlock the page if an I/O error occurs. + ``readpages`` called by the VM to read pages associated with the address_space object. This is essentially just a vector version of readpage. Instead of just one page, several pages are requested. readpages is only used for read-ahead, so read errors are ignored. If anything goes wrong, feel free to give up. + This interface is deprecated and will be removed by the end of + 2020; implement readahead instead. ``write_begin`` Called by the generic buffered write code to ask the filesystem diff --git a/include/linux/fs.h b/include/linux/fs.h index 3cd4fe6b845e..d4e2d2964346 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -292,6 +292,7 @@ enum positive_aop_returns { struct page; struct address_space; struct writeback_control; +struct readahead_control; /* * Write life time hint values. @@ -375,6 +376,7 @@ struct address_space_operations { */ int (*readpages)(struct file *filp, struct address_space *mapping, struct list_head *pages, unsigned nr_pages); + void (*readahead)(struct readahead_control *); int (*write_begin)(struct file *, struct address_space *mapping, loff_t pos, unsigned len, unsigned flags, diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index 4989d330fada..b3008605fd1b 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -669,6 +669,24 @@ static inline struct page *readahead_page(struct readahead_control *rac) return page; } +/* The byte offset into the file of this readahead block */ +static inline loff_t readahead_pos(struct readahead_control *rac) +{ + return (loff_t)rac->_index * PAGE_SIZE; +} + +/* The number of bytes in this readahead block */ +static inline loff_t readahead_length(struct readahead_control *rac) +{ + return (loff_t)rac->_nr_pages * PAGE_SIZE; +} + +/* The index of the first page in this readahead block */ +static inline unsigned int readahead_index(struct readahead_control *rac) +{ + return rac->_index; +} + /* 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 aaa209559ba2..07cdfbf00f4b 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -124,7 +124,14 @@ static void read_pages(struct readahead_control *rac, struct list_head *pages) blk_start_plug(&plug); - if (aops->readpages) { + if (aops->readahead) { + aops->readahead(rac); + /* Clean up the remaining pages */ + while ((page = readahead_page(rac))) { + unlock_page(page); + put_page(page); + } + } else if (aops->readpages) { aops->readpages(rac->file, rac->mapping, pages, readahead_count(rac)); /* Clean up the remaining pages */ @@ -234,7 +241,8 @@ void force_page_cache_readahead(struct address_space *mapping, struct file_ra_state *ra = &filp->f_ra; unsigned long max_pages; - if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages)) + if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages && + !mapping->a_ops->readahead)) return; /*