This patch adds a chapter about kpagecache interface. Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> --- 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>