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From: Josef Bacik <josef@toxicpanda.com>
To: kernel-team@fb.com, linux-kernel@vger.kernel.org,
	hannes@cmpxchg.org, tj@kernel.org, linux-fsdevel@vger.kernel.org,
	akpm@linux-foundation.org, riel@redhat.com, linux-mm@kvack.org,
	linux-btrfs@vger.kernel.org
Subject: [PATCH 6/9] mm: use the cached page for filemap_fault
Date: Wed, 26 Sep 2018 17:08:53 -0400	[thread overview]
Message-ID: <20180926210856.7895-7-josef@toxicpanda.com> (raw)
In-Reply-To: <20180926210856.7895-1-josef@toxicpanda.com>

If we drop the mmap_sem we have to redo the vma lookup which requires
redoing the fault handler.  Chances are we will just come back to the
same page, so save this page in our vmf->cached_page and reuse it in the
next loop through the fault handler.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 mm/filemap.c | 30 ++++++++++++++++++++++++++++--
 1 file changed, 28 insertions(+), 2 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 65395ee132a0..5212ab637832 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2530,13 +2530,38 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
 	pgoff_t offset = vmf->pgoff;
 	int flags = vmf->flags;
 	pgoff_t max_off;
-	struct page *page;
+	struct page *page = NULL;
+	struct page *cached_page = vmf->cached_page;
 	vm_fault_t ret = 0;
 
 	max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
 	if (unlikely(offset >= max_off))
 		return VM_FAULT_SIGBUS;
 
+	/*
+	 * We may have read in the page already and have a page from an earlier
+	 * loop.  If so we need to see if this page is still valid, and if not
+	 * do the whole dance over again.
+	 */
+	if (cached_page) {
+		if (flags & FAULT_FLAG_KILLABLE) {
+			error = lock_page_killable(cached_page);
+			if (error) {
+				up_read(&mm->mmap_sem);
+				goto out_retry;
+			}
+		} else
+			lock_page(cached_page);
+		vmf->cached_page = NULL;
+		if (cached_page->mapping == mapping &&
+		    cached_page->index == offset) {
+			page = cached_page;
+			goto have_cached_page;
+		}
+		unlock_page(cached_page);
+		put_page(cached_page);
+	}
+
 	/*
 	 * Do we have something in the page cache already?
 	 */
@@ -2587,6 +2612,7 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
 		put_page(page);
 		goto retry_find;
 	}
+have_cached_page:
 	VM_BUG_ON_PAGE(page->index != offset, page);
 
 	/*
@@ -2677,7 +2703,7 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
 	if (fpin)
 		fput(fpin);
 	if (page)
-		put_page(page);
+		vmf->cached_page = page;
 	return ret | VM_FAULT_RETRY;
 }
 EXPORT_SYMBOL(filemap_fault);
-- 
2.14.3

  parent reply	other threads:[~2018-09-26 21:08 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-26 21:08 [RFC][PATCH 0/9][V2] drop the mmap_sem when doing IO in the fault path Josef Bacik
2018-09-26 21:08 ` [PATCH 1/9] mm: infrastructure for page fault page caching Josef Bacik
2018-09-27 16:24   ` Matthew Wilcox
2018-09-26 21:08 ` [PATCH 2/9] mm: drop mmap_sem for page cache read IO submission Josef Bacik
2018-09-26 21:08 ` [PATCH 3/9] mm: clean up swapcache lookup and creation function names Josef Bacik
2018-09-26 21:08 ` [PATCH 4/9] mm: drop mmap_sem for swap read IO submission Josef Bacik
2018-09-26 21:08 ` [PATCH 5/9] mm: drop the mmap_sem in all read fault cases Josef Bacik
2018-09-26 21:08 ` Josef Bacik [this message]
2018-09-26 21:08 ` [PATCH 7/9] mm: add a flag to indicate we used a cached page Josef Bacik
2018-09-26 21:08 ` [PATCH 8/9] mm: allow ->page_mkwrite to do retries Josef Bacik
2018-09-26 21:08 ` [PATCH 9/9] btrfs: drop mmap_sem in mkwrite for btrfs Josef Bacik

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