From: =?ISO-8859-15?Q?Luk=E1=A8_Czerner?= Subject: Re: [PATCH 06/12 v2] mm: teach truncate_inode_pages_range() to hadnle non page aligned ranges Date: Tue, 17 Jul 2012 14:16:48 +0200 (CEST) Message-ID: References: <1342185555-21146-1-git-send-email-lczerner@redhat.com> <1342185555-21146-6-git-send-email-lczerner@redhat.com> Mime-Version: 1.0 Content-Type: MULTIPART/MIXED; BOUNDARY="571144193-1991951733-1342527413=:14869" Cc: Hugh Dickins , Andrew Morton , "Theodore Ts'o" , Dave Chinner , linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, achender@linux.vnet.ibm.com To: =?ISO-8859-15?Q?Luk=E1=A8_Czerner?= Return-path: In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. --571144193-1991951733-1342527413=:14869 Content-Type: TEXT/PLAIN; charset=ISO-8859-15 Content-Transfer-Encoding: 8BIT On Tue, 17 Jul 2012, Luk?? Czerner wrote: > Date: Tue, 17 Jul 2012 13:57:42 +0200 (CEST) > From: Luk?? Czerner > To: Hugh Dickins > Cc: Lukas Czerner , > Andrew Morton , Theodore Ts'o , > Dave Chinner , linux-ext4@vger.kernel.org, > linux-fsdevel@vger.kernel.org, achender@linux.vnet.ibm.com > Subject: Re: [PATCH 06/12 v2] mm: teach truncate_inode_pages_range() to hadnle > non page aligned ranges > > On Tue, 17 Jul 2012, Hugh Dickins wrote: > > > Date: Tue, 17 Jul 2012 01:28:08 -0700 (PDT) > > From: Hugh Dickins > > To: Lukas Czerner > > Cc: Andrew Morton , Theodore Ts'o , > > Dave Chinner , linux-ext4@vger.kernel.org, > > linux-fsdevel@vger.kernel.org, achender@linux.vnet.ibm.com > > Subject: Re: [PATCH 06/12 v2] mm: teach truncate_inode_pages_range() to hadnle > > non page aligned ranges > > > > On Fri, 13 Jul 2012, Lukas Czerner wrote: > > > This commit changes truncate_inode_pages_range() so it can handle non > > > page aligned regions of the truncate. Currently we can hit BUG_ON when > > > the end of the range is not page aligned, but he can handle unaligned > > > start of the range. > > > > > > Being able to handle non page aligned regions of the page can help file > > > system punch_hole implementations and save some work, because once we're > > > holding the page we might as well deal with it right away. > > > > > > Signed-off-by: Lukas Czerner > > > Cc: Hugh Dickins > > > > As I said under 02/12, I'd much rather not change from the existing -1 > > convention: I don't think it's wonderful, but I do think it's confusing > > and a waste of effort to change from it; and I'd rather keep the code > > in truncate.c close to what's doing the same job in shmem.c. > > > > Here's what I came up with (and hacked tmpfs to use it without swap > > temporarily, so I could run fsx for an hour to validate it). But you > > can see I've a couple of questions; and probably ought to reduce the > > partial page code duplication once we're sure what should go in there. > > > > Hugh > > Ok. > > > > > [PATCH]... > > > > Apply to truncate_inode_pages_range() the changes 83e4fa9c16e4 ("tmpfs: > > support fallocate FALLOC_FL_PUNCH_HOLE") made to shmem_truncate_range(): > > so the generic function can handle partial end offset for hole-punching. > > > > In doing tmpfs, I became convinced that it needed a set_page_dirty() on > > the partial pages, and I'm doing that here: but perhaps it should be the > > responsibility of the calling filesystem? I don't know. > > In file system, if the range is block aligned we do not need the page to > be dirtied. However if it is not block aligned (at least in ext4) > we're going to handle it ourselves and possibly mark the page buffer > dirty (hence the page would be dirty). Also in case of data > journalling, we'll have to take care of the last block in the hole > ourselves. So I think file systems should take care of dirtying the > partial page if needed. > > > > > And I'm doubtful whether this code can be correct (on a filesystem with > > blocksize less than pagesize) without adding an end offset argument to > > address_space_operations invalidatepage(page, offset): convince me! > > Well, I can't. It really seems that on block size < page size file > systems we could potentially discard dirty buffers beyond the hole > we're punching if it is not page aligned. We would probably need to > add end offset argument to the invalidatepage() aop. However I do not > seem to be able to trigger the problem yet so maybe I'm still > missing something. My bad, it definitely is not safe without the end offset argument in invalidatepage() aops ..sigh.. > > -Lukas > > > > > Not-yet-signed-off-by: Hugh Dickins > > --- > > > > mm/truncate.c | 69 +++++++++++++++++++++++++++++------------------- > > 1 file changed, 42 insertions(+), 27 deletions(-) > > > > --- 3.5-rc7/mm/truncate.c 2012-06-03 06:42:11.249787128 -0700 > > +++ linux/mm/truncate.c 2012-07-16 22:54:16.903821549 -0700 > > @@ -49,14 +49,6 @@ void do_invalidatepage(struct page *page > > (*invalidatepage)(page, offset); > > } > > > > -static inline void truncate_partial_page(struct page *page, unsigned partial) > > -{ > > - zero_user_segment(page, partial, PAGE_CACHE_SIZE); > > - cleancache_invalidate_page(page->mapping, page); > > - if (page_has_private(page)) > > - do_invalidatepage(page, partial); > > -} > > - > > /* > > * This cancels just the dirty bit on the kernel page itself, it > > * does NOT actually remove dirty bits on any mmap's that may be > > @@ -190,8 +182,8 @@ int invalidate_inode_page(struct page *p > > * @lend: offset to which to truncate > > * > > * Truncate the page cache, removing the pages that are between > > - * specified offsets (and zeroing out partial page > > - * (if lstart is not page aligned)). > > + * specified offsets (and zeroing out partial pages > > + * if lstart or lend + 1 is not page aligned). > > * > > * Truncate takes two passes - the first pass is nonblocking. It will not > > * block on page locks and it will not block on writeback. The second pass > > @@ -206,31 +198,32 @@ int invalidate_inode_page(struct page *p > > void truncate_inode_pages_range(struct address_space *mapping, > > loff_t lstart, loff_t lend) > > { > > - const pgoff_t start = (lstart + PAGE_CACHE_SIZE-1) >> PAGE_CACHE_SHIFT; > > - const unsigned partial = lstart & (PAGE_CACHE_SIZE - 1); > > + pgoff_t start = (lstart + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT; > > + pgoff_t end = (lend + 1) >> PAGE_CACHE_SHIFT; > > + unsigned int partial_start = lstart & (PAGE_CACHE_SIZE - 1); > > + unsigned int partial_end = (lend + 1) & (PAGE_CACHE_SIZE - 1); > > struct pagevec pvec; > > pgoff_t index; > > - pgoff_t end; > > int i; > > > > cleancache_invalidate_inode(mapping); > > if (mapping->nrpages == 0) > > return; > > > > - BUG_ON((lend & (PAGE_CACHE_SIZE - 1)) != (PAGE_CACHE_SIZE - 1)); > > - end = (lend >> PAGE_CACHE_SHIFT); > > + if (lend == -1) > > + end = -1; /* unsigned, so actually very big */ > > > > pagevec_init(&pvec, 0); > > index = start; > > - while (index <= end && pagevec_lookup(&pvec, mapping, index, > > - min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1)) { > > + while (index < end && pagevec_lookup(&pvec, mapping, index, > > + min(end - index, (pgoff_t)PAGEVEC_SIZE))) { > > mem_cgroup_uncharge_start(); > > for (i = 0; i < pagevec_count(&pvec); i++) { > > struct page *page = pvec.pages[i]; > > > > /* We rely upon deletion not changing page->index */ > > index = page->index; > > - if (index > end) > > + if (index >= end) > > break; > > > > if (!trylock_page(page)) > > @@ -249,27 +242,51 @@ void truncate_inode_pages_range(struct a > > index++; > > } > > > > - if (partial) { > > + if (partial_start) { > > struct page *page = find_lock_page(mapping, start - 1); > > if (page) { > > + unsigned int top = PAGE_CACHE_SIZE; > > + if (start > end) { > > + top = partial_end; > > + partial_end = 0; > > + } > > wait_on_page_writeback(page); > > - truncate_partial_page(page, partial); > > + zero_user_segment(page, partial_start, top); > > + cleancache_invalidate_page(mapping, page); > > + if (page_has_private(page)) > > + do_invalidatepage(page, partial_start); > > + set_page_dirty(page); > > unlock_page(page); > > page_cache_release(page); > > } > > } > > + if (partial_end) { > > + struct page *page = find_lock_page(mapping, end); > > + if (page) { > > + wait_on_page_writeback(page); > > + zero_user_segment(page, 0, partial_end); > > + cleancache_invalidate_page(mapping, page); > > + if (page_has_private(page)) > > + do_invalidatepage(page, 0); > > + set_page_dirty(page); > > + unlock_page(page); > > + page_cache_release(page); > > + } > > + } > > + if (start >= end) > > + return; > > > > index = start; > > for ( ; ; ) { > > cond_resched(); > > if (!pagevec_lookup(&pvec, mapping, index, > > - min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1)) { > > + min(end - index, (pgoff_t)PAGEVEC_SIZE))) { > > if (index == start) > > break; > > index = start; > > continue; > > } > > - if (index == start && pvec.pages[0]->index > end) { > > + if (index == start && pvec.pages[0]->index >= end) { > > pagevec_release(&pvec); > > break; > > } > > @@ -279,7 +296,7 @@ void truncate_inode_pages_range(struct a > > > > /* We rely upon deletion not changing page->index */ > > index = page->index; > > - if (index > end) > > + if (index >= end) > > break; > > > > lock_page(page); > > @@ -624,10 +641,8 @@ void truncate_pagecache_range(struct ino > > * This rounding is currently just for example: unmap_mapping_range > > * expands its hole outwards, whereas we want it to contract the hole > > * inwards. However, existing callers of truncate_pagecache_range are > > - * doing their own page rounding first; and truncate_inode_pages_range > > - * currently BUGs if lend is not pagealigned-1 (it handles partial > > - * page at start of hole, but not partial page at end of hole). Note > > - * unmap_mapping_range allows holelen 0 for all, and we allow lend -1. > > + * doing their own page rounding first. Note that unmap_mapping_range > > + * allows holelen 0 for all, and we allow lend -1 for end of file. > > */ > > > > /* > > > --571144193-1991951733-1342527413=:14869--