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Registered in England and Wales under Company Registration No. 3798903 Subject: [RFC PATCH v2 3/5] mm: Make swap_readpage() for SWP_FS_OPS use ->direct_IO() not ->readpage() From: David Howells To: willy@infradead.org Cc: dhowells@redhat.com, dhowells@redhat.com, trond.myklebust@primarydata.com, darrick.wong@oracle.com, hch@lst.de, viro@zeniv.linux.org.uk, jlayton@kernel.org, sfrench@samba.org, torvalds@linux-foundation.org, linux-nfs@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Date: Thu, 12 Aug 2021 21:22:24 +0100 Message-ID: <162879974434.3306668.4798886633463058599.stgit@warthog.procyon.org.uk> In-Reply-To: <162879971699.3306668.8977537647318498651.stgit@warthog.procyon.org.uk> References: <162879971699.3306668.8977537647318498651.stgit@warthog.procyon.org.uk> User-Agent: StGit/0.23 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Make swap_readpage(), when accessing a swap file (SWP_FS_OPS) use the ->direct_IO() method on the filesystem rather then ->readpage(). Suggested-by: Matthew Wilcox (Oracle) Signed-off-by: David Howells --- include/linux/fs.h | 1 mm/page_io.c | 115 +++++++++++++++++++++++++++++++++++++++++++++++++--- 2 files changed, 110 insertions(+), 6 deletions(-) diff --git a/include/linux/fs.h b/include/linux/fs.h index b3e6a20f28ef..94c47b9b5b1c 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -336,6 +336,7 @@ struct kiocb { union { unsigned int ki_cookie; /* for ->iopoll */ struct wait_page_queue *ki_waitq; /* for async buffered IO */ + struct page *ki_swap_page; /* For swapfile_read/write */ }; randomized_struct_fields_end diff --git a/mm/page_io.c b/mm/page_io.c index 62cabcdfcec6..92ec4a7b0545 100644 --- a/mm/page_io.c +++ b/mm/page_io.c @@ -26,6 +26,24 @@ #include #include +/* + * Keep track of the kiocb we're using to do async DIO. We have to + * refcount it until various things stop looking at the kiocb *after* + * calling ->ki_complete(). + */ +struct swapfile_kiocb { + struct kiocb iocb; + refcount_t ki_refcnt; +}; + +static void swapfile_put_kiocb(struct swapfile_kiocb *ki) +{ + if (refcount_dec_and_test(&ki->ki_refcnt)) { + fput(ki->iocb.ki_filp); + kfree(ki); + } +} + static void end_swap_bio_write(struct bio *bio) { struct page *page = bio_first_page_all(bio); @@ -353,6 +371,96 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc) return 0; } +static void __swapfile_read_complete(struct kiocb *iocb, long ret, long ret2) +{ + struct page *page = iocb->ki_swap_page; + + if (ret == PAGE_SIZE) { + count_vm_event(PSWPIN); + SetPageUptodate(page); + } else { + SetPageError(page); + pr_err_ratelimited("Read error (%ld) on dio swapfile (%llu)\n", + ret, page_file_offset(page)); + } + + unlock_page(page); +} + +static void swapfile_read_complete(struct kiocb *iocb, long ret, long ret2) +{ + struct swapfile_kiocb *ki = container_of(iocb, struct swapfile_kiocb, iocb); + + __swapfile_read_complete(iocb, ret, ret2); + swapfile_put_kiocb(ki); +} + +static int swapfile_read_sync(struct swap_info_struct *sis, struct page *page) +{ + struct kiocb kiocb; + struct file *swap_file = sis->swap_file; + struct bio_vec bv = { + .bv_page = page, + .bv_len = thp_size(page), + .bv_offset = 0 + }; + struct iov_iter to; + int ret; + + init_sync_kiocb(&kiocb, swap_file); + kiocb.ki_swap_page = page; + kiocb.ki_pos = page_file_offset(page); + kiocb.ki_filp = swap_file; + kiocb.ki_flags = IOCB_DIRECT | IOCB_SWAP; + /* Should set IOCB_HIPRI too, but the box becomes unresponsive whilst + * putting out occasional messages about the NFS sunrpc scheduling + * tasks being hung. + */ + + iov_iter_bvec(&to, READ, &bv, 1, thp_size(page)); + ret = swap_file->f_mapping->a_ops->direct_IO(&kiocb, &to); + + __swapfile_read_complete(&kiocb, ret, 0); + return (ret > 0) ? 0 : ret; +} + +static int swapfile_read(struct swap_info_struct *sis, struct page *page, + bool synchronous) +{ + struct swapfile_kiocb *ki; + struct file *swap_file = sis->swap_file; + struct bio_vec bv = { + .bv_page = page, + .bv_len = thp_size(page), + .bv_offset = 0 + }; + struct iov_iter to; + int ret; + + if (synchronous) + return swapfile_read_sync(sis, page); + + ki = kzalloc(sizeof(*ki), GFP_KERNEL); + if (!ki) + return -ENOMEM; + + refcount_set(&ki->ki_refcnt, 2); + init_sync_kiocb(&ki->iocb, swap_file); + ki->iocb.ki_swap_page = page; + ki->iocb.ki_flags = IOCB_DIRECT | IOCB_SWAP; + ki->iocb.ki_pos = page_file_offset(page); + ki->iocb.ki_filp = get_file(swap_file); + ki->iocb.ki_complete = swapfile_read_complete; + + iov_iter_bvec(&to, READ, &bv, 1, thp_size(page)); + ret = swap_file->f_mapping->a_ops->direct_IO(&ki->iocb, &to); + + if (ret != -EIOCBQUEUED) + swapfile_read_complete(&ki->iocb, ret, 0); + swapfile_put_kiocb(ki); + return (ret > 0) ? 0 : ret; +} + int swap_readpage(struct page *page, bool synchronous) { struct bio *bio; @@ -380,12 +488,7 @@ int swap_readpage(struct page *page, bool synchronous) } if (data_race(sis->flags & SWP_FS_OPS)) { - struct file *swap_file = sis->swap_file; - struct address_space *mapping = swap_file->f_mapping; - - ret = mapping->a_ops->readpage(swap_file, page); - if (!ret) - count_vm_event(PSWPIN); + ret = swapfile_read(sis, page, synchronous); goto out; }