lkml.org 
[lkml]   [2014]   [Mar]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 6/6] Documentation: update Documentation/vm/pagemap.txt
Date
This patch adds a chapter about kpagecache interface.

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
---
Documentation/vm/pagemap.txt | 29 +++++++++++++++++++++++++++++
1 file changed, 29 insertions(+)

diff --git v3.14-rc6.orig/Documentation/vm/pagemap.txt v3.14-rc6/Documentation/vm/pagemap.txt
index 5948e455c4d2..c8039263fc45 100644
--- v3.14-rc6.orig/Documentation/vm/pagemap.txt
+++ v3.14-rc6/Documentation/vm/pagemap.txt
@@ -150,3 +150,32 @@ once.
Reading from any of the files will return -EINVAL if you are not starting
the read on an 8-byte boundary (e.g., if you sought an odd number of bytes
into the file), or if the size of the read is not a multiple of 8 bytes.
+
+
+kpagecache, from file perspective
+---------------------------------
+
+Similarly to pagemap, we have a interface /proc/kpagecache to let userspace
+know about pagecache profile for a given file. Unlike pagemap interface,
+we don't have to mmap() and fault in the target file, so the impact on other
+workloads (maybe profile targets) is minimum.
+
+To use this interface, firstly we open it and write the name of the target
+file to it for setup. And then we can read the pagecache info of the file.
+The file contains the array of 64-bit entries for each page offset. Data
+format is like below:
+
+ * Bits 0-49 page frame number (PFN) if present
+ * Bits 50-59 zero (reserved)
+ * Bits 60-63 pagecache tags
+
+Good example is tools/vm/page-types.c, where we can get the list of pages
+belonging to the file like below:
+
+ $ dd if=/dev/urandom of=file bs=4096 count=2
+ $ date >> file
+ $ tools/vm/page-types -f file -Nl
+ pgoff pfn tags flags
+ 0 3305f 0 __RU_l______________________________
+ 1 374bb 0 __RU_l______________________________
+ 2 6c5ac 1 ___UDlA_____________________________
--
1.8.5.3


\
 
 \ /
  Last update: 2014-03-13 23:22    [W:0.065 / U:0.388 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site