readahead: fault retry breaks mmap file read random detection

.fault now can retry.  The retry can break state machine of .fault.  In
filemap_fault, if page is miss, ra->mmap_miss is increased.  In the second
try, since the page is in page cache now, ra->mmap_miss is decreased.  And
these are done in one fault, so we can't detect random mmap file access.

Add a new flag to indicate .fault is tried once.  In the second try, skip
ra->mmap_miss decreasing.  The filemap_fault state machine is ok with it.

I only tested x86, didn't test other archs, but looks the change for other
archs is obvious, but who knows :)

Signed-off-by: Shaohua Li <shaohua.li@fusionio.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 2 insertions, 0 deletions

diff --git a/arch/sparc/mm/fault_32.c b/arch/sparc/mm/fault_32.c
index 77ac917be152..e98bfda205a2 100644
--- a/arch/sparc/mm/fault_32.c
+++ b/arch/sparc/mm/fault_32.c
@@ -265,6 +265,7 @@ good_area:
                 }
                 if (fault & VM_FAULT_RETRY) {
                         flags &= ~FAULT_FLAG_ALLOW_RETRY;
+                        flags |= FAULT_FLAG_TRIED;
 
                         /* No need to up_read(&mm->mmap_sem) as we would
                          * have already released it in __lock_page_or_retry
diff --git a/arch/sparc/mm/fault_64.c b/arch/sparc/mm/fault_64.c
index 1fe0429b6314..413d29263304 100644
--- a/arch/sparc/mm/fault_64.c
+++ b/arch/sparc/mm/fault_64.c
@@ -452,6 +452,7 @@ good_area:
                 }
                 if (fault & VM_FAULT_RETRY) {
                         flags &= ~FAULT_FLAG_ALLOW_RETRY;
+                        flags |= FAULT_FLAG_TRIED;
 
                         /* No need to up_read(&mm->mmap_sem) as we would
                          * have already released it in __lock_page_or_retry