linux 内存文件系统使用 - tmpfs, ramfs, shmfs

2022-03-04 11:18:25

背景

在做一些测试时，如果IO设备很烂的话，可以直接使用内存文件系统，避免IO上引入的一些开销影响测试结果。

用法很简单：

tmpfs or shmfs

mount a shmfs with a certain size to /dev/shm, and set the correct permissions.

For tmpfs you do not need to specify a size. Tmpfs or shmfs allocated memory is pageable.

For example:

Example Mount shmfs:

# mount -t shm shmfs -o size=20g /dev/shm   
  
Edit /etc/fstab:  
  
shmfs /dev/shm shm size=20g 0 0

Example Mount tmpfs:

# mount –t tmpfs tmpfs /dev/shm   
  
Edit /etc/fstab:  
  
none /dev/shm tmpfs defaults 0 0

ramfs

ramfs is similar to shmfs, except that pages are not pageable or swappable.

This approach provides the commonly desired effect. ramfs is created by:

umount /dev/shm  
  
mount -t ramfs ramfs /dev/shm

例子

[root@pg11-test ~]# mkdir /mnt/tmpfs  
[root@pg11-test ~]# mkdir /mnt/ramfs

1、tmpfs

mount -t tmpfs tmpfs /mnt/tmpfs -o size=10G,noatime,nodiratime,rw  
mkdir /mnt/tmpfs/a  
chmod 777 /mnt/tmpfs/a

2、ramfs

mount -t ramfs ramfs /mnt/ramfs -o noatime,nodiratime,rw,data=writeback,nodelalloc,nobarrier  
mkdir /mnt/ramfs/a  
chmod 777 /mnt/ramfs/a

ramfs无法在mount时限制大小，即使限制了也不起作用，在df结果中也看不到这个挂载点，但是实际上已经挂载。

[root@pg11-test ~]# mount  
tmpfs on /mnt/tmpfs type tmpfs (rw,noatime,nodiratime,size=10485760k)  
ramfs on /mnt/ramfs type ramfs (rw,noatime,nodiratime,data=writeback,nodelalloc,nobarrier)  
  
[root@pg11-test ~]# df -h  
Filesystem                 Size  Used Avail Use% Mounted on  
/dev/vda1                  197G   17G  171G   9% /  
devtmpfs                   252G     0  252G   0% /dev  
tmpfs                      252G  936K  252G   1% /dev/shm  
tmpfs                      252G  676K  252G   1% /run  
tmpfs                      252G     0  252G   0% /sys/fs/cgroup  
/dev/mapper/vgdata01-lv03  4.0T  549G  3.5T  14% /data03  
/dev/mapper/vgdata01-lv02  4.0T  335G  3.7T   9% /data02  
/dev/mapper/vgdata01-lv01  4.0T  1.5T  2.6T  37% /data01  
tmpfs                       51G     0   51G   0% /run/user/0  
/dev/mapper/vgdata01-lv04  2.0T  621G  1.3T  32% /data04  
tmpfs                       10G     0   10G   0% /mnt/tmpfs

内存文件系统性能

PostgreSQL fsync测试接口，测试内存文件系统fsync性能。

su - digoal  
  
  
digoal@pg11-test-> pg_test_fsync -f /mnt/tmpfs/a/1  
5 seconds per test  
O_DIRECT supported on this platform for open_datasync and open_sync.  
  
Compare file sync methods using one 8kB write:  
(in wal_sync_method preference order, except fdatasync is Linux's default)  
        open_datasync                                  n/a*  
        fdatasync                       1137033.436 ops/sec       1 usecs/op  
        fsync                           1146431.736 ops/sec       1 usecs/op  
        fsync_writethrough                              n/a  
        open_sync                                      n/a*  
* This file system and its mount options do not support direct  
  I/O, e.g. ext4 in journaled mode.  
  
Compare file sync methods using two 8kB writes:  
(in wal_sync_method preference order, except fdatasync is Linux's default)  
        open_datasync                                  n/a*  
        fdatasync                        622763.705 ops/sec       2 usecs/op  
        fsync                            625990.998 ops/sec       2 usecs/op  
        fsync_writethrough                              n/a  
        open_sync                                      n/a*  
* This file system and its mount options do not support direct  
  I/O, e.g. ext4 in journaled mode.  
  
Compare open_sync with different write sizes:  
(This is designed to compare the cost of writing 16kB in different write  
open_sync sizes.)  
         1 * 16kB open_sync write                      n/a*  
         2 *  8kB open_sync writes                     n/a*  
         4 *  4kB open_sync writes                     n/a*  
         8 *  2kB open_sync writes                     n/a*  
        16 *  1kB open_sync writes                     n/a*  
  
Test if fsync on non-write file descriptor is honored:  
(If the times are similar, fsync() can sync data written on a different  
descriptor.)  
        write, fsync, close              317779.892 ops/sec       3 usecs/op  
        write, close, fsync              317769.037 ops/sec       3 usecs/op  
  
Non-sync'ed 8kB writes:  
        write                            529490.541 ops/sec       2 usecs/op  
  
digoal@pg11-test-> pg_test_fsync -f /mnt/ramfs/a/1  
5 seconds per test  
O_DIRECT supported on this platform for open_datasync and open_sync.  
  
Compare file sync methods using one 8kB write:  
(in wal_sync_method preference order, except fdatasync is Linux's default)  
        open_datasync                                  n/a*  
        fdatasync                       1146515.453 ops/sec       1 usecs/op  
        fsync                           1149912.760 ops/sec       1 usecs/op  
        fsync_writethrough                              n/a  
        open_sync                                      n/a*  
* This file system and its mount options do not support direct  
  I/O, e.g. ext4 in journaled mode.  
  
Compare file sync methods using two 8kB writes:  
(in wal_sync_method preference order, except fdatasync is Linux's default)  
        open_datasync                                  n/a*  
        fdatasync                        621456.930 ops/sec       2 usecs/op  
        fsync                            624811.200 ops/sec       2 usecs/op  
        fsync_writethrough                              n/a  
        open_sync                                      n/a*  
* This file system and its mount options do not support direct  
  I/O, e.g. ext4 in journaled mode.  
  
Compare open_sync with different write sizes:  
(This is designed to compare the cost of writing 16kB in different write  
open_sync sizes.)  
         1 * 16kB open_sync write                      n/a*  
         2 *  8kB open_sync writes                     n/a*  
         4 *  4kB open_sync writes                     n/a*  
         8 *  2kB open_sync writes                     n/a*  
        16 *  1kB open_sync writes                     n/a*  
  
Test if fsync on non-write file descriptor is honored:  
(If the times are similar, fsync() can sync data written on a different  
descriptor.)  
        write, fsync, close              314754.770 ops/sec       3 usecs/op  
        write, close, fsync              314509.045 ops/sec       3 usecs/op  
  
Non-sync'ed 8kB writes:  
        write                            517299.869 ops/sec       2 usecs/op

本地磁盘性能如下：

digoal@pg11-test-> pg_test_fsync -f /data01/digoal/1  
5 seconds per test  
O_DIRECT supported on this platform for open_datasync and open_sync.  
  
Compare file sync methods using one 8kB write:  
(in wal_sync_method preference order, except fdatasync is Linux's default)  
        open_datasync                     46574.176 ops/sec      21 usecs/op  
        fdatasync                         40183.743 ops/sec      25 usecs/op  
        fsync                             36875.852 ops/sec      27 usecs/op  
        fsync_writethrough                              n/a  
        open_sync                         42927.560 ops/sec      23 usecs/op  
  
Compare file sync methods using two 8kB writes:  
(in wal_sync_method preference order, except fdatasync is Linux's default)  
        open_datasync                     17121.111 ops/sec      58 usecs/op  
        fdatasync                         26438.641 ops/sec      38 usecs/op  
        fsync                             24562.907 ops/sec      41 usecs/op  
        fsync_writethrough                              n/a  
        open_sync                         15698.199 ops/sec      64 usecs/op  
  
Compare open_sync with different write sizes:  
(This is designed to compare the cost of writing 16kB in different write  
open_sync sizes.)  
         1 * 16kB open_sync write         28793.172 ops/sec      35 usecs/op  
         2 *  8kB open_sync writes        15720.156 ops/sec      64 usecs/op  
         4 *  4kB open_sync writes        10007.818 ops/sec     100 usecs/op  
         8 *  2kB open_sync writes         5698.259 ops/sec     175 usecs/op  
        16 *  1kB open_sync writes         3116.232 ops/sec     321 usecs/op  
  
Test if fsync on non-write file descriptor is honored:  
(If the times are similar, fsync() can sync data written on a different  
descriptor.)  
        write, fsync, close               33399.473 ops/sec      30 usecs/op  
        write, close, fsync               33216.001 ops/sec      30 usecs/op  
  
Non-sync'ed 8kB writes:  
        write                            376584.982 ops/sec       3 usecs/op

性能对比，显而易见。