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Subject[PATCH 5/7] mm: add a flag to indicate we used a cached page
Date
This is preparation for dropping the mmap_sem in page_mkwrite.  We need
to know if we used our cached page so we can be sure it is the page we
already did the page_mkwrite stuff on so we don't have to redo all of
that work.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
include/linux/mm.h | 6 +++++-
mm/filemap.c | 5 ++++-
2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 4a84ec976dfc..a7305d193c71 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -318,6 +318,9 @@ extern pgprot_t protection_map[16];
#define FAULT_FLAG_USER 0x40 /* The fault originated in userspace */
#define FAULT_FLAG_REMOTE 0x80 /* faulting for non current tsk/mm */
#define FAULT_FLAG_INSTRUCTION 0x100 /* The fault was during an instruction fetch */
+#define FAULT_FLAG_USED_CACHED 0x200 /* Our vmf->page was from a previous
+ * loop through the fault handler.
+ */

#define FAULT_FLAG_TRACE \
{ FAULT_FLAG_WRITE, "WRITE" }, \
@@ -328,7 +331,8 @@ extern pgprot_t protection_map[16];
{ FAULT_FLAG_TRIED, "TRIED" }, \
{ FAULT_FLAG_USER, "USER" }, \
{ FAULT_FLAG_REMOTE, "REMOTE" }, \
- { FAULT_FLAG_INSTRUCTION, "INSTRUCTION" }
+ { FAULT_FLAG_INSTRUCTION, "INSTRUCTION" }, \
+ { FAULT_FLAG_USED_CACHED, "USED_CACHED" }

/*
* vm_fault is filled by the the pagefault handler and passed to the vma's
diff --git a/mm/filemap.c b/mm/filemap.c
index 5212ab637832..e9cb44bd35aa 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2556,6 +2556,7 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
if (cached_page->mapping == mapping &&
cached_page->index == offset) {
page = cached_page;
+ vmf->flags |= FAULT_FLAG_USED_CACHED;
goto have_cached_page;
}
unlock_page(cached_page);
@@ -2619,8 +2620,10 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
* We have a locked page in the page cache, now we need to check
* that it's up-to-date. If not, it is going to be due to an error.
*/
- if (unlikely(!PageUptodate(page)))
+ if (unlikely(!PageUptodate(page))) {
+ vmf->flags &= ~(FAULT_FLAG_USED_CACHED);
goto page_not_uptodate;
+ }

/*
* Found the page and have a reference on it.
--
2.14.3
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