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mm: consistent truncate and invalidate loops
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Make the pagevec_lookup loops in truncate_inode_pages_range(),
invalidate_mapping_pages() and invalidate_inode_pages2_range() more
consistent with each other.

They were relying upon page->index of an unlocked page, but apologizing
for it: accept it, embrace it, add comments and WARN_ONs, and simplify the
index handling.

invalidate_inode_pages2_range() had special handling for a wrapped
page->index + 1 = 0 case; but MAX_LFS_FILESIZE doesn't let us anywhere
near there, and a corrupt page->index in the radix_tree could cause more
trouble than that would catch.  Remove that wrapped handling.

invalidate_inode_pages2_range() uses min() to limit the pagevec_lookup
when near the end of the range: copy that into the other two, although
it's less useful than you might think (it limits the use of the buffer,
rather than the indices looked up).

Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Hugh Dickins authored and Linus Torvalds committed Jul 26, 2011
1 parent 8a549be commit b85e0ef
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Showing 2 changed files with 49 additions and 63 deletions.
2 changes: 2 additions & 0 deletions mm/filemap.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -128,6 +128,7 @@ void __delete_from_page_cache(struct page *page)

radix_tree_delete(&mapping->page_tree, page->index);
page->mapping = NULL;
/* Leave page->index set: truncation lookup relies upon it */
mapping->nrpages--;
__dec_zone_page_state(page, NR_FILE_PAGES);
if (PageSwapBacked(page))
Expand Down Expand Up @@ -483,6 +484,7 @@ int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
spin_unlock_irq(&mapping->tree_lock);
} else {
page->mapping = NULL;
/* Leave page->index set: truncation relies upon it */
spin_unlock_irq(&mapping->tree_lock);
mem_cgroup_uncharge_cache_page(page);
page_cache_release(page);
Expand Down
110 changes: 47 additions & 63 deletions mm/truncate.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -199,9 +199,6 @@ int invalidate_inode_page(struct page *page)
* The first pass will remove most pages, so the search cost of the second pass
* is low.
*
* When looking at page->index outside the page lock we need to be careful to
* copy it into a local to avoid races (it could change at any time).
*
* 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.
Expand All @@ -210,10 +207,10 @@ 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;
pgoff_t end;
const unsigned partial = lstart & (PAGE_CACHE_SIZE - 1);
struct pagevec pvec;
pgoff_t next;
pgoff_t index;
pgoff_t end;
int i;

cleancache_flush_inode(mapping);
Expand All @@ -224,24 +221,21 @@ void truncate_inode_pages_range(struct address_space *mapping,
end = (lend >> PAGE_CACHE_SHIFT);

pagevec_init(&pvec, 0);
next = start;
while (next <= end &&
pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
index = start;
while (index <= end && pagevec_lookup(&pvec, mapping, index,
min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1)) {
mem_cgroup_uncharge_start();
for (i = 0; i < pagevec_count(&pvec); i++) {
struct page *page = pvec.pages[i];
pgoff_t page_index = page->index;

if (page_index > end) {
next = page_index;
/* We rely upon deletion not changing page->index */
index = page->index;
if (index > end)
break;
}

if (page_index > next)
next = page_index;
next++;
if (!trylock_page(page))
continue;
WARN_ON(page->index != index);
if (PageWriteback(page)) {
unlock_page(page);
continue;
Expand All @@ -252,6 +246,7 @@ void truncate_inode_pages_range(struct address_space *mapping,
pagevec_release(&pvec);
mem_cgroup_uncharge_end();
cond_resched();
index++;
}

if (partial) {
Expand All @@ -264,13 +259,14 @@ void truncate_inode_pages_range(struct address_space *mapping,
}
}

next = start;
index = start;
for ( ; ; ) {
cond_resched();
if (!pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
if (next == start)
if (!pagevec_lookup(&pvec, mapping, index,
min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1)) {
if (index == start)
break;
next = start;
index = start;
continue;
}
if (pvec.pages[0]->index > end) {
Expand All @@ -281,18 +277,20 @@ void truncate_inode_pages_range(struct address_space *mapping,
for (i = 0; i < pagevec_count(&pvec); i++) {
struct page *page = pvec.pages[i];

if (page->index > end)
/* We rely upon deletion not changing page->index */
index = page->index;
if (index > end)
break;

lock_page(page);
WARN_ON(page->index != index);
wait_on_page_writeback(page);
truncate_inode_page(mapping, page);
if (page->index > next)
next = page->index;
next++;
unlock_page(page);
}
pagevec_release(&pvec);
mem_cgroup_uncharge_end();
index++;
}
cleancache_flush_inode(mapping);
}
Expand Down Expand Up @@ -333,35 +331,26 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping,
pgoff_t start, pgoff_t end)
{
struct pagevec pvec;
pgoff_t next = start;
pgoff_t index = start;
unsigned long ret;
unsigned long count = 0;
int i;

pagevec_init(&pvec, 0);
while (next <= end &&
pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
while (index <= end && pagevec_lookup(&pvec, mapping, index,
min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1)) {
mem_cgroup_uncharge_start();
for (i = 0; i < pagevec_count(&pvec); i++) {
struct page *page = pvec.pages[i];
pgoff_t index;
int lock_failed;

lock_failed = !trylock_page(page);

/*
* We really shouldn't be looking at the ->index of an
* unlocked page. But we're not allowed to lock these
* pages. So we rely upon nobody altering the ->index
* of this (pinned-by-us) page.
*/
/* We rely upon deletion not changing page->index */
index = page->index;
if (index > next)
next = index;
next++;
if (lock_failed)
continue;
if (index > end)
break;

if (!trylock_page(page))
continue;
WARN_ON(page->index != index);
ret = invalidate_inode_page(page);
unlock_page(page);
/*
Expand All @@ -371,12 +360,11 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping,
if (!ret)
deactivate_page(page);
count += ret;
if (next > end)
break;
}
pagevec_release(&pvec);
mem_cgroup_uncharge_end();
cond_resched();
index++;
}
return count;
}
Expand Down Expand Up @@ -442,56 +430,51 @@ int invalidate_inode_pages2_range(struct address_space *mapping,
pgoff_t start, pgoff_t end)
{
struct pagevec pvec;
pgoff_t next;
pgoff_t index;
int i;
int ret = 0;
int ret2 = 0;
int did_range_unmap = 0;
int wrapped = 0;

cleancache_flush_inode(mapping);
pagevec_init(&pvec, 0);
next = start;
while (next <= end && !wrapped &&
pagevec_lookup(&pvec, mapping, next,
min(end - next, (pgoff_t)PAGEVEC_SIZE - 1) + 1)) {
index = start;
while (index <= end && pagevec_lookup(&pvec, mapping, index,
min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1)) {
mem_cgroup_uncharge_start();
for (i = 0; i < pagevec_count(&pvec); i++) {
struct page *page = pvec.pages[i];
pgoff_t page_index;

/* We rely upon deletion not changing page->index */
index = page->index;
if (index > end)
break;

lock_page(page);
WARN_ON(page->index != index);
if (page->mapping != mapping) {
unlock_page(page);
continue;
}
page_index = page->index;
next = page_index + 1;
if (next == 0)
wrapped = 1;
if (page_index > end) {
unlock_page(page);
break;
}
wait_on_page_writeback(page);
if (page_mapped(page)) {
if (!did_range_unmap) {
/*
* Zap the rest of the file in one hit.
*/
unmap_mapping_range(mapping,
(loff_t)page_index<<PAGE_CACHE_SHIFT,
(loff_t)(end - page_index + 1)
<< PAGE_CACHE_SHIFT,
(loff_t)index << PAGE_CACHE_SHIFT,
(loff_t)(1 + end - index)
<< PAGE_CACHE_SHIFT,
0);
did_range_unmap = 1;
} else {
/*
* Just zap this page
*/
unmap_mapping_range(mapping,
(loff_t)page_index<<PAGE_CACHE_SHIFT,
PAGE_CACHE_SIZE, 0);
(loff_t)index << PAGE_CACHE_SHIFT,
PAGE_CACHE_SIZE, 0);
}
}
BUG_ON(page_mapped(page));
Expand All @@ -507,6 +490,7 @@ int invalidate_inode_pages2_range(struct address_space *mapping,
pagevec_release(&pvec);
mem_cgroup_uncharge_end();
cond_resched();
index++;
}
cleancache_flush_inode(mapping);
return ret;
Expand Down

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