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| -rw-r--r-- | Documentation/filesystems/proc.txt | 105 |
1 files changed, 105 insertions, 0 deletions
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt index 72af5de1effb..5484ab5efd4f 100644 --- a/Documentation/filesystems/proc.txt +++ b/Documentation/filesystems/proc.txt @@ -41,6 +41,7 @@ Table of Contents 2.11 /proc/sys/fs/mqueue - POSIX message queues filesystem 2.12 /proc/<pid>/oom_adj - Adjust the oom-killer score 2.13 /proc/<pid>/oom_score - Display current oom-killer score + 2.14 /proc/<pid>/io - Display the IO accounting fields ------------------------------------------------------------------------------ Preface @@ -1990,3 +1991,107 @@ need to recompile the kernel, or even to reboot the system. The files in the command to write value into these files, thereby changing the default settings of the kernel. ------------------------------------------------------------------------------ + +2.14 /proc/<pid>/io - Display the IO accounting fields +------------------------------------------------------- + +This file contains IO statistics for each running process + +Example +------- + +test:/tmp # dd if=/dev/zero of=/tmp/test.dat & +[1] 3828 + +test:/tmp # cat /proc/3828/io +rchar: 323934931 +wchar: 323929600 +syscr: 632687 +syscw: 632675 +read_bytes: 0 +write_bytes: 323932160 +cancelled_write_bytes: 0 + + +Description +----------- + +rchar +----- + +I/O counter: chars read +The number of bytes which this task has caused to be read from storage. This +is simply the sum of bytes which this process passed to read() and pread(). +It includes things like tty IO and it is unaffected by whether or not actual +physical disk IO was required (the read might have been satisfied from +pagecache) + + +wchar +----- + +I/O counter: chars written +The number of bytes which this task has caused, or shall cause to be written +to disk. Similar caveats apply here as with rchar. + + +syscr +----- + +I/O counter: read syscalls +Attempt to count the number of read I/O operations, i.e. syscalls like read() +and pread(). + + +syscw +----- + +I/O counter: write syscalls +Attempt to count the number of write I/O operations, i.e. syscalls like +write() and pwrite(). + + +read_bytes +---------- + +I/O counter: bytes read +Attempt to count the number of bytes which this process really did cause to +be fetched from the storage layer. Done at the submit_bio() level, so it is +accurate for block-backed filesystems. <please add status regarding NFS and +CIFS at a later time> + + +write_bytes +----------- + +I/O counter: bytes written +Attempt to count the number of bytes which this process caused to be sent to +the storage layer. This is done at page-dirtying time. + + +cancelled_write_bytes +--------------------- + +The big inaccuracy here is truncate. If a process writes 1MB to a file and +then deletes the file, it will in fact perform no writeout. But it will have +been accounted as having caused 1MB of write. +In other words: The number of bytes which this process caused to not happen, +by truncating pagecache. A task can cause "negative" IO too. If this task +truncates some dirty pagecache, some IO which another task has been accounted +for (in it's write_bytes) will not be happening. We _could_ just subtract that +from the truncating task's write_bytes, but there is information loss in doing +that. + + +Note +---- + +At its current implementation state, this is a bit racy on 32-bit machines: if +process A reads process B's /proc/pid/io while process B is updating one of +those 64-bit counters, process A could see an intermediate result. + + +More information about this can be found within the taskstats documentation in +Documentation/accounting. + +------------------------------------------------------------------------------ |
