What is dentries and Inodes ?

[redhat70]

Hi,

To clear the cache memory, we use the following commands :

Flush file system buffers by executing,

# sync : what does sync command Do ? Why should we use it before using the # echo 1 > /proc/sys/vm/drop_caches ?

To free page cache:

# echo 1 > /proc/sys/vm/drop_caches

To free dentries and inodes:

# echo 2 > /proc/sys/vm/drop_caches

To free page cache, dentries and inodes:

echo 3 > /proc/sys/vm/drop_caches


What is dentries and Inodes ?


Can any body explain this Please....?



Regards,
Aparna.

[Jonathan183]

try here ...

[Lakshmipathi]

Jonathan183 link should give lot of info. Here is some short info about them.

# sync : what does sync command Do ?

sync flushes the buffer into disk.It forces completion of pending disk writes.


create 10000 files like

mkdir test && for i in {1..10000};do date > test/$i ;done

Now do

time cat test/*

Note the sys time.Run the time cat test/* again.Check sys time,is that reduced ? that because of page cache.

Now drop page cache

# echo 1 > /proc/sys/vm/drop_caches

Now run time cat test/* again.See its increased.


Do the similar thing run

time ls -l test

Note the sys time,run it again ,you should see
time decreasing.

Now drop the caches of dentries and inodes:

# echo 2 > /proc/sys/vm/drop_caches

Run check ls time again.


cache in general is used for performance optimization.i.e no need to go and fetch the data from hard-disk.It will place the frequently accessed data into physical memory
itself.

HTH