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[23.128.96.18]) by mx.google.com with ESMTP id n19si365536edv.187.2020.11.24.18.34.38; Tue, 24 Nov 2020 18:35:01 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=casper.20170209 header.b=g0HDyhda; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726776AbgKYCcq (ORCPT + 99 others); Tue, 24 Nov 2020 21:32:46 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42324 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725952AbgKYCcp (ORCPT ); Tue, 24 Nov 2020 21:32:45 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 41618C0613D4; Tue, 24 Nov 2020 18:32:45 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=P2TSdtkfgK7WesR1VipqV2PSDW2NVNCUIStDCNxcMGE=; b=g0HDyhdaQ2GWERfKQYYtUgfneH 8IYnjCKMGGYjFG7vjJY/SC1JqP8PuKyTR8Bsa9p4TmZEiX2oRQgAAutLavqzW0N3DVXzSc3mg1YUC JTvxN367R27Sv2azAr3S6dYJQoUc1P2mRtcAX3JiNT/60aTFIYPGyBvHz92Af+QAADxUrTdxgcUqX 3jNNTUY+efnqSe1l8U2sF+YrSgPPS4MmM+2Nr4Zpmbggm83EdMTwJjrVtT6QwPCRzUT/YzYKg40Ip zUbdrJ+MUBVx+yWT6EHz2IJiBLTnv02xKbT4cpcA1iDmiHqC357AQRqghJgPXwqJp7ZotPtDp3f65 N8rS9VDg==; Received: from willy by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1khkbi-0003Z5-N9; Wed, 25 Nov 2020 02:32:34 +0000 Date: Wed, 25 Nov 2020 02:32:34 +0000 From: Matthew Wilcox To: Hugh Dickins Cc: Andrew Morton , Jan Kara , William Kucharski , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, hch@lst.de, hannes@cmpxchg.org, yang.shi@linux.alibaba.com, dchinner@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 00/16] Overhaul multi-page lookups for THP Message-ID: <20201125023234.GH4327@casper.infradead.org> References: <20201112212641.27837-1-willy@infradead.org> <20201117153947.GL29991@casper.infradead.org> <20201117191513.GV29991@casper.infradead.org> <20201117234302.GC29991@casper.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201117234302.GC29991@casper.infradead.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 17, 2020 at 11:43:02PM +0000, Matthew Wilcox wrote: > On Tue, Nov 17, 2020 at 07:15:13PM +0000, Matthew Wilcox wrote: > > I find both of these functions exceptionally confusing. Does this > > make it easier to understand? > > Never mind, this is buggy. I'll send something better tomorrow. That took a week, not a day. *sigh*. At least this is shorter. commit 1a02863ce04fd325922d6c3db6d01e18d55f966b Author: Matthew Wilcox (Oracle) Date: Tue Nov 17 10:45:18 2020 -0500 fix mm-truncateshmem-handle-truncates-that-split-thps.patch diff --git a/mm/internal.h b/mm/internal.h index 75ae680d0a2c..4ac239e8c42c 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -622,5 +622,6 @@ struct migration_target_control { gfp_t gfp_mask; }; -bool truncate_inode_partial_page(struct page *page, loff_t start, loff_t end); +pgoff_t truncate_inode_partial_page(struct address_space *mapping, + struct page *page, loff_t start, loff_t end); #endif /* __MM_INTERNAL_H */ diff --git a/mm/shmem.c b/mm/shmem.c index 5da4f1a3e663..6fd00948e592 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -866,26 +866,33 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend, { struct address_space *mapping = inode->i_mapping; struct shmem_inode_info *info = SHMEM_I(inode); - pgoff_t start = (lstart + PAGE_SIZE - 1) >> PAGE_SHIFT; - pgoff_t end = (lend + 1) >> PAGE_SHIFT; + pgoff_t start, end; struct pagevec pvec; pgoff_t indices[PAGEVEC_SIZE]; struct page *page; long nr_swaps_freed = 0; pgoff_t index; int i; - bool partial_end; - if (lend == -1) - end = -1; /* unsigned, so actually very big */ + page = NULL; + start = lstart >> PAGE_SHIFT; + shmem_getpage(inode, start, &page, SGP_READ); + if (page) { + page = thp_head(page); + set_page_dirty(page); + start = truncate_inode_partial_page(mapping, page, lstart, + lend); + } + + /* 'end' includes a partial page */ + end = lend / PAGE_SIZE; pagevec_init(&pvec); index = start; while (index < end && find_lock_entries(mapping, index, end - 1, - &pvec, indices)) { + &pvec, indices)) { for (i = 0; i < pagevec_count(&pvec); i++) { page = pvec.pages[i]; - index = indices[i]; if (xa_is_value(page)) { @@ -895,8 +902,6 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend, index, page); continue; } - index += thp_nr_pages(page) - 1; - if (!unfalloc || !PageUptodate(page)) truncate_inode_page(mapping, page); unlock_page(page); @@ -907,85 +912,60 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend, index++; } - partial_end = ((lend + 1) % PAGE_SIZE) > 0; - page = NULL; - shmem_getpage(inode, lstart >> PAGE_SHIFT, &page, SGP_READ); - if (page) { - bool same_page; - - page = thp_head(page); - same_page = lend < page_offset(page) + thp_size(page); - if (same_page) - partial_end = false; - set_page_dirty(page); - if (!truncate_inode_partial_page(page, lstart, lend)) { - start = page->index + thp_nr_pages(page); - if (same_page) - end = page->index; - } - unlock_page(page); - put_page(page); - page = NULL; - } - - if (partial_end) - shmem_getpage(inode, end, &page, SGP_READ); - if (page) { - page = thp_head(page); - set_page_dirty(page); - if (!truncate_inode_partial_page(page, lstart, lend)) - end = page->index; - unlock_page(page); - put_page(page); - } - index = start; - while (index < end) { + while (index <= end) { cond_resched(); - if (!find_get_entries(mapping, index, end - 1, &pvec, - indices)) { + if (!find_get_entries(mapping, index, end, &pvec, indices)) { /* If all gone or hole-punch or unfalloc, we're done */ - if (index == start || end != -1) + if (index == start || lend != (loff_t)-1) break; /* But if truncating, restart to make sure all gone */ index = start; continue; } + for (i = 0; i < pagevec_count(&pvec); i++) { page = pvec.pages[i]; - index = indices[i]; if (xa_is_value(page)) { if (unfalloc) continue; - if (shmem_free_swap(mapping, index, page)) { - /* Swap was replaced by page: retry */ - index--; - break; + index = indices[i]; + if (index == end) { + /* Partial page swapped out? */ + shmem_getpage(inode, end, &page, + SGP_READ); + } else { + if (shmem_free_swap(mapping, index, + page)) { + /* Swap replaced: retry */ + break; + } + nr_swaps_freed++; + continue; } - nr_swaps_freed++; - continue; + } else { + lock_page(page); } - lock_page(page); - if (!unfalloc || !PageUptodate(page)) { if (page_mapping(page) != mapping) { /* Page was replaced by swap: retry */ unlock_page(page); - index--; + put_page(page); break; } VM_BUG_ON_PAGE(PageWriteback(page), page); - truncate_inode_page(mapping, page); + index = truncate_inode_partial_page(mapping, + page, lstart, lend); + if (index > end) + end = indices[i] - 1; } - index = page->index + thp_nr_pages(page) - 1; - unlock_page(page); } + index = indices[i - 1] + 1; pagevec_remove_exceptionals(&pvec); - pagevec_release(&pvec); - index++; + pagevec_reinit(&pvec); } spin_lock_irq(&info->lock); diff --git a/mm/truncate.c b/mm/truncate.c index ddb94fc0bc9e..e9fb4f1db837 100644 --- a/mm/truncate.c +++ b/mm/truncate.c @@ -225,19 +225,20 @@ int truncate_inode_page(struct address_space *mapping, struct page *page) } /* - * Handle partial (transparent) pages. The page may be entirely within the - * range if a split has raced with us. If not, we zero the part of the - * page that's within the [start, end] range, and then split the page if - * it's a THP. split_page_range() will discard pages which now lie beyond - * i_size, and we rely on the caller to discard pages which lie within a + * Handle partial (transparent) pages. If the page is entirely within + * the range, we discard it. If not, we split the page if it's a THP + * and zero the part of the page that's within the [start, end] range. + * split_page_range() will discard any of the subpages which now lie + * beyond i_size, and the caller will discard pages which lie within a * newly created hole. * - * Returns false if THP splitting failed so the caller can avoid - * discarding the entire page which is stubbornly unsplit. + * Return: The index after the current page. */ -bool truncate_inode_partial_page(struct page *page, loff_t start, loff_t end) +pgoff_t truncate_inode_partial_page(struct address_space *mapping, + struct page *page, loff_t start, loff_t end) { loff_t pos = page_offset(page); + pgoff_t next_index = page->index + thp_nr_pages(page); unsigned int offset, length; if (pos < start) @@ -251,24 +252,33 @@ bool truncate_inode_partial_page(struct page *page, loff_t start, loff_t end) length = end + 1 - pos - offset; wait_on_page_writeback(page); - if (length == thp_size(page)) { - truncate_inode_page(page->mapping, page); - return true; - } - - /* - * We may be zeroing pages we're about to discard, but it avoids - * doing a complex calculation here, and then doing the zeroing - * anyway if the page split fails. - */ - zero_user(page, offset, length); + if (length == thp_size(page)) + goto truncate; cleancache_invalidate_page(page->mapping, page); if (page_has_private(page)) do_invalidatepage(page, offset, length); if (!PageTransHuge(page)) - return true; - return split_huge_page(page) == 0; + goto zero; + page += offset / PAGE_SIZE; + if (split_huge_page(page) < 0) { + page -= offset / PAGE_SIZE; + goto zero; + } + next_index = page->index + 1; + offset %= PAGE_SIZE; + if (offset == 0 && length >= PAGE_SIZE) + goto truncate; + length = PAGE_SIZE - offset; +zero: + zero_user(page, offset, length); + goto out; +truncate: + truncate_inode_page(mapping, page); +out: + unlock_page(page); + put_page(page); + return next_index; } /* @@ -322,10 +332,6 @@ int invalidate_inode_page(struct page *page) * The first pass will remove most pages, so the search cost of the second pass * is low. * - * We pass down the cache-hot hint to the page freeing code. Even if the - * mapping is large, it is probably the case that the final pages are the most - * recently touched, and freeing happens in ascending file offset order. - * * Note that since ->invalidatepage() accepts range to invalidate * truncate_inode_pages_range is able to handle cases where lend + 1 is not * page aligned properly. @@ -333,34 +339,24 @@ int invalidate_inode_page(struct page *page) void truncate_inode_pages_range(struct address_space *mapping, loff_t lstart, loff_t lend) { - pgoff_t start; /* inclusive */ - pgoff_t end; /* exclusive */ + pgoff_t start, end; struct pagevec pvec; pgoff_t indices[PAGEVEC_SIZE]; pgoff_t index; int i; struct page * page; - bool partial_end; if (mapping->nrpages == 0 && mapping->nrexceptional == 0) goto out; - /* - * 'start' and 'end' always covers the range of pages to be fully - * truncated. Partial pages are covered with 'partial_start' at the - * start of the range and 'partial_end' at the end of the range. - * Note that 'end' is exclusive while 'lend' is inclusive. - */ - start = (lstart + PAGE_SIZE - 1) >> PAGE_SHIFT; - if (lend == -1) - /* - * lend == -1 indicates end-of-file so we have to set 'end' - * to the highest possible pgoff_t and since the type is - * unsigned we're using -1. - */ - end = -1; - else - end = (lend + 1) >> PAGE_SHIFT; + start = lstart >> PAGE_SHIFT; + page = find_lock_head(mapping, start); + if (page) + start = truncate_inode_partial_page(mapping, page, lstart, + lend); + + /* 'end' includes a partial page */ + end = lend / PAGE_SIZE; pagevec_init(&pvec); index = start; @@ -377,37 +373,11 @@ void truncate_inode_pages_range(struct address_space *mapping, cond_resched(); } - partial_end = ((lend + 1) % PAGE_SIZE) > 0; - page = find_lock_head(mapping, lstart >> PAGE_SHIFT); - if (page) { - bool same_page = lend < page_offset(page) + thp_size(page); - if (same_page) - partial_end = false; - if (!truncate_inode_partial_page(page, lstart, lend)) { - start = page->index + thp_nr_pages(page); - if (same_page) - end = page->index; - } - unlock_page(page); - put_page(page); - page = NULL; - } - - if (partial_end) - page = find_lock_head(mapping, end); - if (page) { - if (!truncate_inode_partial_page(page, lstart, lend)) - end = page->index; - unlock_page(page); - put_page(page); - } - index = start; - while (index < end) { + while (index <= end) { cond_resched(); - if (!find_get_entries(mapping, index, end - 1, &pvec, - indices)) { + if (!find_get_entries(mapping, index, end, &pvec, indices)) { /* If all gone from start onwards, we're done */ if (index == start) break; @@ -418,22 +388,19 @@ void truncate_inode_pages_range(struct address_space *mapping, for (i = 0; i < pagevec_count(&pvec); i++) { page = pvec.pages[i]; - - /* We rely upon deletion not changing page->index */ - index = indices[i]; - if (xa_is_value(page)) continue; lock_page(page); - index = page->index + thp_nr_pages(page) - 1; - wait_on_page_writeback(page); - truncate_inode_page(mapping, page); - unlock_page(page); + index = truncate_inode_partial_page(mapping, page, + lstart, lend); + /* Couldn't split a THP? */ + if (index > end) + end = indices[i] - 1; } + index = indices[i - 1] + 1; truncate_exceptional_pvec_entries(mapping, &pvec, indices); - pagevec_release(&pvec); - index++; + pagevec_reinit(&pvec); } out: