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From: Hugh Dickins <hughd@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>,
	Shakeel Butt <shakeelb@google.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Yang Shi <shy828301@gmail.com>, Miaohe Lin <linmiaohe@huawei.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Michal Hocko <mhocko@suse.com>, Rik van Riel <riel@surriel.com>,
	Christoph Hellwig <hch@infradead.org>,
	Matthew Wilcox <willy@infradead.org>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Alexey Gladkov <legion@kernel.org>,
	Chris Wilson <chris@chris-wilson.co.uk>,
	Matthew Auld <matthew.auld@intel.com>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-api@vger.kernel.org, linux-mm@kvack.org
Subject: [PATCH 01/16] huge tmpfs: fix fallocate(vanilla) advance over huge pages
Date: Fri, 30 Jul 2021 00:25:37 -0700 (PDT)	[thread overview]
Message-ID: <af71608e-ecc-af95-3511-1a62cbf8d751@google.com> (raw)
In-Reply-To: <2862852d-badd-7486-3a8e-c5ea9666d6fb@google.com>

shmem_fallocate() goes to a lot of trouble to leave its newly allocated
pages !Uptodate, partly to identify and undo them on failure, partly to
leave the overhead of clearing them until later.  But the huge page case
did not skip to the end of the extent, walked through the tail pages one
by one, and appeared to work just fine: but in doing so, cleared and
Uptodated the huge page, so there was no way to undo it on failure.

Now advance immediately to the end of the huge extent, with a comment on
why this is more than just an optimization.  But although this speeds up
huge tmpfs fallocation, it does leave the clearing until first use, and
some users may have come to appreciate slow fallocate but fast first use:
if they complain, then we can consider adding a pass to clear at the end.

Fixes: 800d8c63b2e9 ("shmem: add huge pages support")
Signed-off-by: Hugh Dickins <hughd@google.com>
---
 mm/shmem.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 70d9ce294bb4..0cd5c9156457 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2736,7 +2736,7 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
 	inode->i_private = &shmem_falloc;
 	spin_unlock(&inode->i_lock);
 
-	for (index = start; index < end; index++) {
+	for (index = start; index < end; ) {
 		struct page *page;
 
 		/*
@@ -2759,13 +2759,26 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
 			goto undone;
 		}
 
+		index++;
+		/*
+		 * Here is a more important optimization than it appears:
+		 * a second SGP_FALLOC on the same huge page will clear it,
+		 * making it PageUptodate and un-undoable if we fail later.
+		 */
+		if (PageTransCompound(page)) {
+			index = round_up(index, HPAGE_PMD_NR);
+			/* Beware 32-bit wraparound */
+			if (!index)
+				index--;
+		}
+
 		/*
 		 * Inform shmem_writepage() how far we have reached.
 		 * No need for lock or barrier: we have the page lock.
 		 */
-		shmem_falloc.next++;
 		if (!PageUptodate(page))
-			shmem_falloc.nr_falloced++;
+			shmem_falloc.nr_falloced += index - shmem_falloc.next;
+		shmem_falloc.next = index;
 
 		/*
 		 * If !PageUptodate, leave it that way so that freeable pages
-- 
2.26.2


  reply	other threads:[~2021-07-30  7:25 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-30  7:22 [PATCH 00/16] tmpfs: HUGEPAGE and MEM_LOCK fcntls and memfds Hugh Dickins
2021-07-30  7:25 ` Hugh Dickins [this message]
2021-07-30 21:36   ` [PATCH 01/16] huge tmpfs: fix fallocate(vanilla) advance over huge pages Yang Shi
2021-08-01  3:38     ` Hugh Dickins
2021-08-02 20:36       ` Yang Shi
2021-07-30  7:28 ` [PATCH 02/16] huge tmpfs: fix split_huge_page() after FALLOC_FL_KEEP_SIZE Hugh Dickins
2021-07-30 23:48   ` Yang Shi
2021-07-30  7:30 ` [PATCH 03/16] huge tmpfs: remove shrinklist addition from shmem_setattr() Hugh Dickins
2021-07-30 21:50   ` Yang Shi
2021-07-30  7:36 ` [PATCH 04/16] huge tmpfs: revert shmem's use of transhuge_vma_enabled() Hugh Dickins
2021-07-30 21:56   ` Yang Shi
2021-08-01  4:01     ` Hugh Dickins
2021-08-02 20:39       ` Yang Shi
2021-07-30  7:39 ` [PATCH 05/16] huge tmpfs: move shmem_huge_enabled() upwards Hugh Dickins
2021-07-30 21:57   ` Yang Shi
2021-07-30  7:42 ` [PATCH 06/16] huge tmpfs: shmem_is_huge(vma, inode, index) Hugh Dickins
2021-07-30 23:34   ` Yang Shi
2021-08-01  5:22     ` Hugh Dickins
2021-08-01  5:37       ` Hugh Dickins
2021-08-02 21:14       ` Yang Shi
2021-08-04  8:28         ` Hugh Dickins
2021-08-04 19:01           ` Yang Shi
2021-08-06  5:21             ` Hugh Dickins
2021-08-06 17:41               ` Yang Shi
2021-08-05 23:04         ` Yang Shi
2021-08-06  5:43           ` Hugh Dickins
2021-08-06 17:57             ` Yang Shi
2021-08-12 18:19               ` Yang Shi
2021-07-30  7:45 ` [PATCH 07/16] memfd: memfd_create(name, MFD_HUGEPAGE) for shmem huge pages Hugh Dickins
2021-08-04 14:03   ` Kirill A. Shutemov
2021-08-06  3:33     ` Hugh Dickins
2021-07-30  7:48 ` [PATCH 08/16] huge tmpfs: fcntl(fd, F_HUGEPAGE) and fcntl(fd, F_NOHUGEPAGE) Hugh Dickins
2021-08-04 14:08   ` Kirill A. Shutemov
2021-08-06  4:34     ` Hugh Dickins
2021-07-30  7:51 ` [PATCH 09/16] huge tmpfs: decide stat.st_blksize by shmem_is_huge() Hugh Dickins
2021-07-30 23:40   ` Yang Shi
2021-07-30  7:55 ` [PATCH 10/16] tmpfs: fcntl(fd, F_MEM_LOCK) to memlock a tmpfs file Hugh Dickins
2021-08-03  1:38   ` Matthew Wilcox
2021-08-04  9:15     ` Hugh Dickins
2021-07-30  7:57 ` [PATCH 11/16] tmpfs: fcntl(fd, F_MEM_LOCKED) to test if memlocked Hugh Dickins
2021-07-30  8:00 ` [PATCH 12/16] tmpfs: refuse memlock when fallocated beyond i_size Hugh Dickins
2021-07-30  8:03 ` [PATCH 13/16] mm: bool user_shm_lock(loff_t size, struct ucounts *) Hugh Dickins
2021-07-30  8:06 ` [PATCH 14/16] mm: user_shm_lock(,,getuc) and user_shm_unlock(,,putuc) Hugh Dickins
2021-07-30  8:09 ` [PATCH 15/16] tmpfs: permit changing size of memlocked file Hugh Dickins
2021-07-30  8:13 ` [PATCH 16/16] memfd: memfd_create(name, MFD_MEM_LOCK) for memlocked shmem Hugh Dickins

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