mm/gup: decrement head page once for group of subpages

mainline inclusion
from mainline-5.13-rc1
commit 31b912de
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I408MI
CVE: NA

-------------------------------------------------

Rather than decrementing the head page refcount one by one, we walk the
page array and checking which belong to the same compound_head.  Later on
we decrement the calculated amount of references in a single write to the
head page.  To that end switch to for_each_compound_head() does most of
the work.

set_page_dirty() needs no adjustment as it's a nop for non-dirty head
pages and it doesn't operate on tail pages.

This considerably improves unpinning of pages with THP and hugetlbfs:

 - THP

   gup_test -t -m 16384 -r 10 [-L|-a] -S -n 512 -w
   PIN_LONGTERM_BENCHMARK (put values): ~87.6k us -> ~23.2k us

- 16G with 1G huge page size

  gup_test -f /mnt/huge/file -m 16384 -r 10 [-L|-a] -S -n 512 -w
  PIN_LONGTERM_BENCHMARK: (put values): ~87.6k us -> ~27.5k us

Link: https://lkml.kernel.org/r/20210212130843.13865-3-joao.m.martins@oracle.comSigned-off-by: NJoao Martins <joao.m.martins@oracle.com>
Reviewed-by: NJohn Hubbard <jhubbard@nvidia.com>
Reviewed-by: NJason Gunthorpe <jgg@nvidia.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Doug Ledford <dledford@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NChengyang Fan <cy.fan@huawei.com>
Reviewed-by: NChen Wandun <chenwandun@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

mm/gup.c

@@ -266,20 +266,15 @@ void unpin_user_pages_dirty_lock(struct page **pages, unsigned long npages,
 				 bool make_dirty)
 {
 	unsigned long index;
-
-	/*
-	 * TODO: this can be optimized for huge pages: if a series of pages is
-	 * physically contiguous and part of the same compound page, then a
-	 * single operation to the head page should suffice.
-	 */
+	struct page *head;
+	unsigned int ntails;
 
 	if (!make_dirty) {
 		unpin_user_pages(pages, npages);
 		return;
 	}
 
-	for (index = 0; index < npages; index++) {
-		struct page *page = compound_head(pages[index]);
+	for_each_compound_head(index, pages, npages, head, ntails) {
 		/*
 		 * Checking PageDirty at this point may race with
 		 * clear_page_dirty_for_io(), but that's OK. Two key
@@ -300,9 +295,9 @@ void unpin_user_pages_dirty_lock(struct page **pages, unsigned long npages,
 		 * written back, so it gets written back again in the
 		 * next writeback cycle. This is harmless.
 		 */
-		if (!PageDirty(page))
-			set_page_dirty_lock(page);
-		unpin_user_page(page);
+		if (!PageDirty(head))
+			set_page_dirty_lock(head);
+		put_compound_head(head, ntails, FOLL_PIN);
 	}
 }
 EXPORT_SYMBOL(unpin_user_pages_dirty_lock);
@@ -319,6 +314,8 @@ EXPORT_SYMBOL(unpin_user_pages_dirty_lock);
 void unpin_user_pages(struct page **pages, unsigned long npages)
 {
 	unsigned long index;
+	struct page *head;
+	unsigned int ntails;
 
 	/*
 	 * If this WARN_ON() fires, then the system *might* be leaking pages (by
@@ -327,13 +324,9 @@ void unpin_user_pages(struct page **pages, unsigned long npages)
 	 */
 	if (WARN_ON(IS_ERR_VALUE(npages)))
 		return;
-	/*
-	 * TODO: this can be optimized for huge pages: if a series of pages is
-	 * physically contiguous and part of the same compound page, then a
-	 * single operation to the head page should suffice.
-	 */
-	for (index = 0; index < npages; index++)
-		unpin_user_page(pages[index]);
+
+	for_each_compound_head(index, pages, npages, head, ntails)
+		put_compound_head(head, ntails, FOLL_PIN);
 }
 EXPORT_SYMBOL(unpin_user_pages);