From: Zi Yan <[email protected]> To minimize the number of pages after a truncation, when truncating a THP, we do not need to split it all the way down to order-0. The THP has at most three parts, the part before offset, the part to be truncated, the part left at the end. Use the non-zero minimum of them to decide what order we split the THP to.
Signed-off-by: Zi Yan <[email protected]> --- mm/truncate.c | 29 +++++++++++++++++++++++++++-- 1 file changed, 27 insertions(+), 2 deletions(-) diff --git a/mm/truncate.c b/mm/truncate.c index 20bd17538ec2..2e93d702f2c6 100644 --- a/mm/truncate.c +++ b/mm/truncate.c @@ -237,7 +237,9 @@ int truncate_inode_page(struct address_space *mapping, struct page *page) bool truncate_inode_partial_page(struct page *page, loff_t start, loff_t end) { loff_t pos = page_offset(page); - unsigned int offset, length; + unsigned int offset, length, remaining, min_subpage_size = PAGE_SIZE; + unsigned int new_order; + if (pos < start) offset = start - pos; @@ -248,6 +250,7 @@ bool truncate_inode_partial_page(struct page *page, loff_t start, loff_t end) length = length - offset; else length = end + 1 - pos - offset; + remaining = thp_size(page) - offset - length; wait_on_page_writeback(page); if (length == thp_size(page)) { @@ -267,7 +270,29 @@ bool truncate_inode_partial_page(struct page *page, loff_t start, loff_t end) do_invalidatepage(page, offset, length); if (!PageTransHuge(page)) return true; - return split_huge_page(page) == 0; + + /* + * find the non-zero minimum of offset, length, and remaining and use it + * to decide the new order of the page after split + */ + if (offset && remaining) + min_subpage_size = min_t(unsigned int, + min_t(unsigned int, offset, length), + remaining); + else if (!offset) + min_subpage_size = min_t(unsigned int, length, remaining); + else /* remaining == 0 */ + min_subpage_size = min_t(unsigned int, length, offset); + + min_subpage_size = max_t(unsigned int, PAGE_SIZE, min_subpage_size); + + new_order = ilog2(min_subpage_size/PAGE_SIZE); + + /* order-1 THP not supported, downgrade to order-0 */ + if (new_order == 1) + new_order = 0; + + return split_huge_page_to_list_to_order(page, NULL, new_order) == 0; } /* -- 2.28.0
