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Message-ID: <alpine.LSU.2.00.1208192144260.2390@eggly.anvils>
Date: Sun, 19 Aug 2012 21:52:48 -0700 (PDT)
From: Hugh Dickins <hughd@...gle.com>
To: Lukas Czerner <lczerner@...hat.com>
cc: linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
tytso@....edu, linux-mmc@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 06/15] mm: teach truncate_inode_pages_range() to handle
non page aligned ranges
On Fri, 27 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 we 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.
>
> In order for this to work correctly, called must register
> invalidatepage_range address space operation, or rely solely on the
> block_invalidatepage_range. That said it will BUG_ON() if caller
> implements invalidatepage(), does not implement invalidatepage_range()
> and use truncate_inode_pages_range() with unaligned end of the range.
>
> This was based on the code provided by Hugh Dickins with some small
> changes to make use of do_invalidatepage_range().
>
> Signed-off-by: Lukas Czerner <lczerner@...hat.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Hugh Dickins <hughd@...gle.com>
Acked-by: Hugh Dickins <hughd@...gle.com>
This looks good to me. I like the way you provide the same args
to do_invalidatepage_range() as to zero_user_segment():
zero_user_segment(page, partial_start, top);
if (page_has_private(page))
do_invalidatepage_range(page, partial_start, top);
Unfortunately, that is not what patches 01-05 are expecting...
Hugh
> ---
> mm/truncate.c | 77 +++++++++++++++++++++++++++++++++++++--------------------
> 1 files changed, 50 insertions(+), 27 deletions(-)
>
> diff --git a/mm/truncate.c b/mm/truncate.c
> index e29e5ea..1f6ea8b 100644
> --- a/mm/truncate.c
> +++ b/mm/truncate.c
> @@ -71,14 +71,6 @@ void do_invalidatepage_range(struct page *page, unsigned long offset,
> #endif
> }
>
> -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
> @@ -212,8 +204,8 @@ int invalidate_inode_page(struct page *page)
> * @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
> @@ -224,35 +216,44 @@ int invalidate_inode_page(struct page *page)
> * 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 it is able to handle cases where lend + 1 is not page aligned.
> + * However in order for this to work caller have to register
> + * invalidatepage_range address space operation or rely solely on
> + * block_invalidatepage_range(). That said, do_invalidatepage_range() will
> + * BUG_ON() if caller implements invalidatapage(), does not implement
invalidatepage()
> + * invalidatepage_range() and uses truncate_inode_pages_range() with lend + 1
> + * unaligned to the page cache size.
> */
> 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))
> @@ -271,27 +272,51 @@ void truncate_inode_pages_range(struct address_space *mapping,
> 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);
> + zero_user_segment(page, partial_start, top);
> + cleancache_invalidate_page(mapping, page);
> + if (page_has_private(page))
> + do_invalidatepage_range(page, partial_start,
> + top);
> + 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);
> - truncate_partial_page(page, partial);
> + zero_user_segment(page, 0, partial_end);
> + cleancache_invalidate_page(mapping, page);
> + if (page_has_private(page))
> + do_invalidatepage_range(page, 0,
> + partial_end);
> 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;
> }
> @@ -301,7 +326,7 @@ void truncate_inode_pages_range(struct address_space *mapping,
>
> /* We rely upon deletion not changing page->index */
> index = page->index;
> - if (index > end)
> + if (index >= end)
> break;
>
> lock_page(page);
> @@ -646,10 +671,8 @@ void truncate_pagecache_range(struct inode *inode, loff_t lstart, loff_t lend)
> * 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.
> */
>
> /*
> --
> 1.7.7.6
>
>
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