From patchwork Sat Oct 17 20:10:55 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kent Overstreet X-Patchwork-Id: 11842977 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 42D191580 for ; Sat, 17 Oct 2020 20:11:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 280A72075E for ; Sat, 17 Oct 2020 20:11:22 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="stHdPGw+" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2439713AbgJQULH (ORCPT ); Sat, 17 Oct 2020 16:11:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46118 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2439678AbgJQULG (ORCPT ); Sat, 17 Oct 2020 16:11:06 -0400 Received: from mail-il1-x144.google.com (mail-il1-x144.google.com [IPv6:2607:f8b0:4864:20::144]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C53F6C061755; Sat, 17 Oct 2020 13:11:06 -0700 (PDT) Received: by mail-il1-x144.google.com with SMTP id l16so6398837ilj.9; Sat, 17 Oct 2020 13:11:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=I2HTdHUjGksNurF6c8jj/TqT2hOjm1bZIM6AKpACqag=; b=stHdPGw+XninTpDUS8RQvmt0MYfa6Ym0tLVnH4c2fhJeaVyVJxEUlS9zV/pBZHjSxJ K+oGqDy63+FBJnNM3Ep13Nxpx/N+9wX8D/uyrBPlsivyrTcYmLUXIUn4iEO++0cgvByY x3r2HVs84LKePtyeOmr0VLNlFdpPF1XXPUOo2yaAfo8FW7xZe8v7rvNa2w2j4WpySsfB fEdikhCDTwCNEnnNygNDlaX5+GY3knYnF9ArcjhnfxchWmDPR31LUBqSDc/Va4aZVX8i 88Aqcx/LvZyh7JbjwwR1lcauAPD47StMqFQDK6evAzeoAPtRsJupgoSLZjWzODEj3UT5 jY1Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=I2HTdHUjGksNurF6c8jj/TqT2hOjm1bZIM6AKpACqag=; b=XYYYjDuUgyawrMjjxZHpdthniIFV5faJmR3V4aq/So8+rJZXImmQgJIR03dX0Kd42t PnYjm3zL9vP4DCTxGvluYnr9ZQZzOp1Og1kqexdPASlHy1ISMuGx6i9+RmcB9D0CBPTG bS1li55jvliz+/dNi552Sbd/cpxs5eCEHqdvaxw/+7z5obLzd4aL1WjiwXNnt0kNp2DQ HtgkWD18hC/avZ5aifbhF2xFEzvftBdJb0umwXZHCd5g0jeFybqaWLJygz8WPhbW1Smg TWicBIvMd4yhgLr/W4fR8Mb5pGL93uWOfWtMCYXiEvyxMSPIhxwNRw4cwP0/sfN0SLDe lGGw== X-Gm-Message-State: AOAM530OOuHeflc/9B8dyA6ZGzkbgNRHiGW2i8081bxlemGm6jjBI8zr zJWo7peP/HNGHXWlqByDRO3C7Re3bg== X-Google-Smtp-Source: ABdhPJyTFdG8q/4Y4gVVl0yCLfq97cm8Y3feGzrEIYfVCNhpOsUc2hUOBjsyemOKiSsJ/gXXF/bxoA== X-Received: by 2002:a92:98c5:: with SMTP id a66mr6834896ill.50.1602965465742; Sat, 17 Oct 2020 13:11:05 -0700 (PDT) Received: from zaphod.evilpiepirate.org ([2601:19b:c500:a1:d1eb:cfce:9b0b:f9e0]) by smtp.gmail.com with ESMTPSA id e204sm5583483iof.16.2020.10.17.13.11.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 17 Oct 2020 13:11:05 -0700 (PDT) From: Kent Overstreet To: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, akpm@linux-foundation.org Cc: Kent Overstreet , willy@infradead.org Subject: [PATCH 2/2] fs: generic_file_buffered_read() now uses find_get_pages_contig Date: Sat, 17 Oct 2020 16:10:55 -0400 Message-Id: <20201017201055.2216969-3-kent.overstreet@gmail.com> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20201017201055.2216969-1-kent.overstreet@gmail.com> References: <20201017201055.2216969-1-kent.overstreet@gmail.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Convert generic_file_buffered_read() to get pages to read from in batches, and then copy data to userspace from many pages at once - in particular, we now don't touch any cachelines that might be contended while we're in the loop to copy data to userspace. This is is a performance improvement on workloads that do buffered reads with large blocksizes, and a very large performance improvement if that file is also being accessed concurrently by different threads. On smaller reads (512 bytes), there's a very small performance improvement (1%, within the margin of error). Signed-off-by: Kent Overstreet Reviewed-by: Jens Axboe --- mm/filemap.c | 300 +++++++++++++++++++++++++++++---------------------- 1 file changed, 172 insertions(+), 128 deletions(-) diff --git a/mm/filemap.c b/mm/filemap.c index 482fd75d66..8cf5b5d9e6 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2148,67 +2148,6 @@ static int lock_page_for_iocb(struct kiocb *iocb, struct page *page) return lock_page_killable(page); } -static int generic_file_buffered_read_page_ok(struct kiocb *iocb, - struct iov_iter *iter, - struct page *page) -{ - struct address_space *mapping = iocb->ki_filp->f_mapping; - struct inode *inode = mapping->host; - struct file_ra_state *ra = &iocb->ki_filp->f_ra; - unsigned int offset = iocb->ki_pos & ~PAGE_MASK; - unsigned int bytes, copied; - loff_t isize, end_offset; - - BUG_ON(iocb->ki_pos >> PAGE_SHIFT != page->index); - - /* - * i_size must be checked after we know the page is Uptodate. - * - * Checking i_size after the check allows us to calculate - * the correct value for "bytes", which means the zero-filled - * part of the page is not copied back to userspace (unless - * another truncate extends the file - this is desired though). - */ - - isize = i_size_read(inode); - if (unlikely(iocb->ki_pos >= isize)) - return 1; - - end_offset = min_t(loff_t, isize, iocb->ki_pos + iter->count); - - bytes = min_t(loff_t, end_offset - iocb->ki_pos, PAGE_SIZE - offset); - - /* If users can be writing to this page using arbitrary - * virtual addresses, take care about potential aliasing - * before reading the page on the kernel side. - */ - if (mapping_writably_mapped(mapping)) - flush_dcache_page(page); - - /* - * Ok, we have the page, and it's up-to-date, so - * now we can copy it to user space... - */ - - copied = copy_page_to_iter(page, offset, bytes, iter); - - iocb->ki_pos += copied; - - /* - * When a sequential read accesses a page several times, - * only mark it as accessed the first time. - */ - if (iocb->ki_pos >> PAGE_SHIFT != ra->prev_pos >> PAGE_SHIFT) - mark_page_accessed(page); - - ra->prev_pos = iocb->ki_pos; - - if (copied < bytes) - return -EFAULT; - - return !iov_iter_count(iter) || iocb->ki_pos == isize; -} - static struct page * generic_file_buffered_read_readpage(struct kiocb *iocb, struct file *filp, @@ -2366,6 +2305,92 @@ generic_file_buffered_read_no_cached_page(struct kiocb *iocb, return generic_file_buffered_read_readpage(iocb, filp, mapping, page); } +static int generic_file_buffered_read_get_pages(struct kiocb *iocb, + struct iov_iter *iter, + struct page **pages, + unsigned int nr) +{ + struct file *filp = iocb->ki_filp; + struct address_space *mapping = filp->f_mapping; + struct file_ra_state *ra = &filp->f_ra; + pgoff_t index = iocb->ki_pos >> PAGE_SHIFT; + pgoff_t last_index = (iocb->ki_pos + iter->count + PAGE_SIZE-1) >> PAGE_SHIFT; + int i, j, nr_got, err = 0; + + nr = min_t(unsigned long, last_index - index, nr); +find_page: + if (fatal_signal_pending(current)) + return -EINTR; + + nr_got = find_get_pages_contig(mapping, index, nr, pages); + if (nr_got) + goto got_pages; + + if (iocb->ki_flags & IOCB_NOIO) + return -EAGAIN; + + page_cache_sync_readahead(mapping, ra, filp, index, last_index - index); + + nr_got = find_get_pages_contig(mapping, index, nr, pages); + if (nr_got) + goto got_pages; + + pages[0] = generic_file_buffered_read_no_cached_page(iocb, iter); + err = PTR_ERR_OR_ZERO(pages[0]); + if (!IS_ERR_OR_NULL(pages[0])) + nr_got = 1; +got_pages: + for (i = 0; i < nr_got; i++) { + struct page *page = pages[i]; + pgoff_t pg_index = index + i; + loff_t pg_pos = max(iocb->ki_pos, + (loff_t) pg_index << PAGE_SHIFT); + loff_t pg_count = iocb->ki_pos + iter->count - pg_pos; + + if (PageReadahead(page)) { + if (iocb->ki_flags & IOCB_NOIO) { + for (j = i; j < nr_got; j++) + put_page(pages[j]); + nr_got = i; + err = -EAGAIN; + break; + } + page_cache_async_readahead(mapping, ra, filp, page, + pg_index, last_index - pg_index); + } + + if (!PageUptodate(page)) { + if ((iocb->ki_flags & IOCB_NOWAIT) || + ((iocb->ki_flags & IOCB_WAITQ) && i)) { + for (j = i; j < nr_got; j++) + put_page(pages[j]); + nr_got = i; + err = -EAGAIN; + break; + } + + page = generic_file_buffered_read_pagenotuptodate(iocb, + filp, iter, page, pg_pos, pg_count); + if (IS_ERR_OR_NULL(page)) { + for (j = i + 1; j < nr_got; j++) + put_page(pages[j]); + nr_got = i; + err = PTR_ERR_OR_ZERO(page); + break; + } + } + } + + if (likely(nr_got)) + return nr_got; + if (err) + return err; + /* + * No pages and no error means we raced and should retry: + */ + goto find_page; +} + /** * generic_file_buffered_read - generic file read routine * @iocb: the iocb to read @@ -2386,96 +2411,115 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb, struct iov_iter *iter, ssize_t written) { struct file *filp = iocb->ki_filp; + struct file_ra_state *ra = &filp->f_ra; struct address_space *mapping = filp->f_mapping; struct inode *inode = mapping->host; - struct file_ra_state *ra = &filp->f_ra; - size_t orig_count = iov_iter_count(iter); - pgoff_t last_index; - int error = 0; + struct page *pages_onstack[PAGEVEC_SIZE], **pages = NULL; + unsigned int nr_pages = min_t(unsigned int, 512, + ((iocb->ki_pos + iter->count + PAGE_SIZE - 1) >> PAGE_SHIFT) - + (iocb->ki_pos >> PAGE_SHIFT)); + int i, pg_nr, error = 0; + bool writably_mapped; + loff_t isize, end_offset; if (unlikely(iocb->ki_pos >= inode->i_sb->s_maxbytes)) return 0; iov_iter_truncate(iter, inode->i_sb->s_maxbytes); - last_index = (iocb->ki_pos + iter->count + PAGE_SIZE-1) >> PAGE_SHIFT; + if (nr_pages > ARRAY_SIZE(pages_onstack)) + pages = kmalloc_array(nr_pages, sizeof(void *), GFP_KERNEL); - for (;;) { - pgoff_t index = iocb->ki_pos >> PAGE_SHIFT; - struct page *page; + if (!pages) { + pages = pages_onstack; + nr_pages = min_t(unsigned int, nr_pages, ARRAY_SIZE(pages_onstack)); + } + do { cond_resched(); -find_page: - if (fatal_signal_pending(current)) { - error = -EINTR; - goto out; - } /* * We can't return -EIOCBQUEUED once we've done some work, so * ensure we don't block: */ - if ((iocb->ki_flags & IOCB_WAITQ) && - (written + orig_count - iov_iter_count(iter))) + if ((iocb->ki_flags & IOCB_WAITQ) && written) iocb->ki_flags |= IOCB_NOWAIT; - page = find_get_page(mapping, index); - if (!page) { - if (iocb->ki_flags & IOCB_NOIO) - goto would_block; - page_cache_sync_readahead(mapping, - ra, filp, - index, last_index - index); - page = find_get_page(mapping, index); - if (unlikely(page == NULL)) { - page = generic_file_buffered_read_no_cached_page(iocb, iter); - if (!page) - goto find_page; - if (IS_ERR(page)) { - error = PTR_ERR(page); - goto out; - } - } - } - if (PageReadahead(page)) { - if (iocb->ki_flags & IOCB_NOIO) { - put_page(page); - goto out; - } - page_cache_async_readahead(mapping, - ra, filp, page, - index, last_index - index); - } - if (!PageUptodate(page)) { - if (iocb->ki_flags & IOCB_NOWAIT) { - put_page(page); - error = -EAGAIN; - goto out; - } - page = generic_file_buffered_read_pagenotuptodate(iocb, - filp, iter, page, iocb->ki_pos, iter->count); - if (!page) - goto find_page; - if (IS_ERR(page)) { - error = PTR_ERR(page); - goto out; - } + i = 0; + pg_nr = generic_file_buffered_read_get_pages(iocb, iter, + pages, nr_pages); + if (pg_nr < 0) { + error = pg_nr; + break; } - error = generic_file_buffered_read_page_ok(iocb, iter, page); - put_page(page); + /* + * i_size must be checked after we know the pages are Uptodate. + * + * Checking i_size after the check allows us to calculate + * the correct value for "nr", which means the zero-filled + * part of the page is not copied back to userspace (unless + * another truncate extends the file - this is desired though). + */ + isize = i_size_read(inode); + if (unlikely(iocb->ki_pos >= isize)) + goto put_pages; - if (error) { - if (error > 0) - error = 0; - goto out; + end_offset = min_t(loff_t, isize, iocb->ki_pos + iter->count); + + while ((iocb->ki_pos >> PAGE_SHIFT) + pg_nr > + (end_offset + PAGE_SIZE - 1) >> PAGE_SHIFT) + put_page(pages[--pg_nr]); + + /* + * Once we start copying data, we don't want to be touching any + * cachelines that might be contended: + */ + writably_mapped = mapping_writably_mapped(mapping); + + /* + * When a sequential read accesses a page several times, only + * mark it as accessed the first time. + */ + if (iocb->ki_pos >> PAGE_SHIFT != + ra->prev_pos >> PAGE_SHIFT) + mark_page_accessed(pages[0]); + for (i = 1; i < pg_nr; i++) + mark_page_accessed(pages[i]); + + for (i = 0; i < pg_nr; i++) { + unsigned int offset = iocb->ki_pos & ~PAGE_MASK; + unsigned int bytes = min_t(loff_t, end_offset - iocb->ki_pos, + PAGE_SIZE - offset); + unsigned int copied; + + /* + * If users can be writing to this page using arbitrary + * virtual addresses, take care about potential aliasing + * before reading the page on the kernel side. + */ + if (writably_mapped) + flush_dcache_page(pages[i]); + + copied = copy_page_to_iter(pages[i], offset, bytes, iter); + + written += copied; + iocb->ki_pos += copied; + ra->prev_pos = iocb->ki_pos; + + if (copied < bytes) { + error = -EFAULT; + break; + } } - } +put_pages: + for (i = 0; i < pg_nr; i++) + put_page(pages[i]); + } while (iov_iter_count(iter) && iocb->ki_pos < isize && !error); -would_block: - error = -EAGAIN; -out: file_accessed(filp); - written += orig_count - iov_iter_count(iter); + + if (pages != pages_onstack) + kfree(pages); return written ? written : error; }