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SubjectRe: [PATCH v2] page cache: Store only head pages in i_pages
On Thu, Feb 14, 2019 at 04:30:04PM +0300, Kirill A. Shutemov wrote:
> - page_cache_delete_batch() will blow up on
>
> VM_BUG_ON_PAGE(page->index + HPAGE_PMD_NR - tail_pages
> != pvec->pages[i]->index, page);

Quite right. I decided to rewrite page_cache_delete_batch. What do you
(and Jan!) think to this? Compile-tested only.

diff --git a/mm/filemap.c b/mm/filemap.c
index 0d71b1acf811..facaa6913ffa 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -279,11 +279,11 @@ EXPORT_SYMBOL(delete_from_page_cache);
* @pvec: pagevec with pages to delete
*
* The function walks over mapping->i_pages and removes pages passed in @pvec
- * from the mapping. The function expects @pvec to be sorted by page index.
+ * from the mapping. The function expects @pvec to be sorted by page index
+ * and is optimised for it to be dense.
* It tolerates holes in @pvec (mapping entries at those indices are not
* modified). The function expects only THP head pages to be present in the
- * @pvec and takes care to delete all corresponding tail pages from the
- * mapping as well.
+ * @pvec.
*
* The function expects the i_pages lock to be held.
*/
@@ -292,40 +292,36 @@ static void page_cache_delete_batch(struct address_space *mapping,
{
XA_STATE(xas, &mapping->i_pages, pvec->pages[0]->index);
int total_pages = 0;
- int i = 0, tail_pages = 0;
+ int i = 0;
struct page *page;

mapping_set_update(&xas, mapping);
xas_for_each(&xas, page, ULONG_MAX) {
- if (i >= pagevec_count(pvec) && !tail_pages)
+ if (i >= pagevec_count(pvec))
break;
+
+ /* A swap/dax/shadow entry got inserted? Skip it. */
if (xa_is_value(page))
continue;
- if (!tail_pages) {
- /*
- * Some page got inserted in our range? Skip it. We
- * have our pages locked so they are protected from
- * being removed.
- */
- if (page != pvec->pages[i]) {
- VM_BUG_ON_PAGE(page->index >
- pvec->pages[i]->index, page);
- continue;
- }
- WARN_ON_ONCE(!PageLocked(page));
- if (PageTransHuge(page) && !PageHuge(page))
- tail_pages = HPAGE_PMD_NR - 1;
+ /*
+ * A page got inserted in our range? Skip it. We have our
+ * pages locked so they are protected from being removed.
+ */
+ if (page != pvec->pages[i]) {
+ VM_BUG_ON_PAGE(page->index > pvec->pages[i]->index,
+ page);
+ continue;
+ }
+
+ WARN_ON_ONCE(!PageLocked(page));
+
+ if (page->index == xas.xa_index)
page->mapping = NULL;
- /*
- * Leave page->index set: truncation lookup relies
- * upon it
- */
+ /* Leave page->index set: truncation lookup relies on it */
+
+ if (page->index + (1UL << compound_order(page)) - 1 ==
+ xas.xa_index)
i++;
- } else {
- VM_BUG_ON_PAGE(page->index + HPAGE_PMD_NR - tail_pages
- != pvec->pages[i]->index, page);
- tail_pages--;
- }
xas_store(&xas, NULL);
total_pages++;
}
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