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) <willy@xxxxxxxxxxxxx>
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:
