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Subject[PATCH v5 30/39] mm: Handle truncates that split large pages
Date
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

Move shmem_punch_compound() to truncate.c and rename it to punch_thp().
Change its arguments to loff_t to make calling do_invalidatepage()
easier. Call it when we find a THP in the cache.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
mm/internal.h | 2 ++
mm/shmem.c | 30 ++--------------------------
mm/truncate.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++++--
3 files changed, 57 insertions(+), 30 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index 5efb13d5c226..3090e22b984d 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -604,4 +604,6 @@ static inline bool is_migrate_highatomic_page(struct page *page)

void setup_zone_pageset(struct zone *zone);
extern struct page *alloc_new_node_page(struct page *page, unsigned long node);
+
+bool punch_thp(struct page *page, loff_t start, loff_t end);
#endif /* __MM_INTERNAL_H */
diff --git a/mm/shmem.c b/mm/shmem.c
index d722eb830317..a4d4e817a33f 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -788,32 +788,6 @@ void shmem_unlock_mapping(struct address_space *mapping)
}
}

-/*
- * Check whether a hole-punch or truncation needs to split a huge page,
- * returning true if no split was required, or the split has been successful.
- *
- * Eviction (or truncation to 0 size) should never need to split a huge page;
- * but in rare cases might do so, if shmem_undo_range() failed to trylock on
- * head, and then succeeded to trylock on tail.
- *
- * A split can only succeed when there are no additional references on the
- * huge page: so the split below relies upon find_get_entries() having stopped
- * when it found a subpage of the huge page, without getting further references.
- */
-static bool shmem_punch_compound(struct page *page, pgoff_t start, pgoff_t end)
-{
- if (!PageTransCompound(page))
- return true;
-
- /* Just proceed to delete a huge page wholly within the range punched */
- if (PageHead(page) &&
- page->index >= start && page->index + HPAGE_PMD_NR <= end)
- return true;
-
- /* Try to split huge page, so we can truly punch the hole or truncate */
- return split_huge_page(page) >= 0;
-}
-
/*
* Remove range of pages and swap entries from page cache, and free them.
* If !unfalloc, truncate or punch hole; if unfalloc, undo failed fallocate.
@@ -867,7 +841,7 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
if ((!unfalloc || !PageUptodate(page)) &&
page_mapping(page) == mapping) {
VM_BUG_ON_PAGE(PageWriteback(page), page);
- if (shmem_punch_compound(page, start, end))
+ if (punch_thp(page, lstart, lend))
truncate_inode_page(mapping, page);
}
unlock_page(page);
@@ -950,7 +924,7 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
break;
}
VM_BUG_ON_PAGE(PageWriteback(page), page);
- if (shmem_punch_compound(page, start, end))
+ if (punch_thp(page, lstart, lend))
truncate_inode_page(mapping, page);
else {
/* Wipe the page and don't get stuck */
diff --git a/mm/truncate.c b/mm/truncate.c
index dad384a4dc6d..59cae74b152d 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -229,6 +229,55 @@ int truncate_inode_page(struct address_space *mapping, struct page *page)
return 0;
}

+/*
+ * Check whether a hole-punch or truncation needs to split a huge page,
+ * returning true if no split was required, or the split has been
+ * successful.
+ *
+ * Eviction (or truncation to 0 size) should never need to split a huge
+ * page; but in rare cases might do so, if shmem_undo_range() failed to
+ * trylock on head, and then succeeded to trylock on tail.
+ *
+ * A split can only succeed when there are no additional references on
+ * the huge page: so the split below relies upon find_get_entries()
+ * having stopped when it found a subpage of the huge page, without
+ * getting further references.
+ */
+bool punch_thp(struct page *page, loff_t start, loff_t end)
+{
+ struct page *head = compound_head(page);
+ loff_t pos = page_offset(head);
+ unsigned int offset, length;
+
+ if (!PageTransCompound(page))
+ return true;
+
+ if (pos < start)
+ offset = start - pos;
+ else
+ offset = 0;
+ length = thp_size(head);
+ if (pos + length < end)
+ length = length - offset;
+ else
+ length = end - pos - offset;
+
+ /* Just proceed to delete a huge page wholly within the range punched */
+ if (length == thp_size(head))
+ return true;
+
+ /*
+ * We're going to split the page into order-0 pages. Tell the
+ * filesystem which range of the page is going to be punched out
+ * so it can discard unnecessary private data.
+ */
+ if (page_has_private(head))
+ do_invalidatepage(head, offset, length);
+
+ /* Try to split huge page, so we can truly punch the hole or truncate */
+ return split_huge_page(page) >= 0;
+}
+
/*
* Used to get rid of pages on hardware memory corruption.
*/
@@ -359,7 +408,8 @@ void truncate_inode_pages_range(struct address_space *mapping,
unlock_page(page);
continue;
}
- pagevec_add(&locked_pvec, page);
+ if (punch_thp(page, lstart, lend))
+ pagevec_add(&locked_pvec, page);
}
for (i = 0; i < pagevec_count(&locked_pvec); i++)
truncate_cleanup_page(mapping, locked_pvec.pages[i]);
@@ -446,7 +496,8 @@ void truncate_inode_pages_range(struct address_space *mapping,
lock_page(page);
WARN_ON(page_to_index(page) != index);
wait_on_page_writeback(page);
- truncate_inode_page(mapping, page);
+ if (punch_thp(page, lstart, lend))
+ truncate_inode_page(mapping, page);
unlock_page(page);
}
truncate_exceptional_pvec_entries(mapping, &pvec, indices, end);
--
2.26.2
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