Subject: Re: swap space for a memory based filesystem
To: Perry E. Metzger <>
From: None <>
List: tech-userlevel
Date: 03/04/2004 09:41:59

 I was confused by the free memory going down, -:(
 but after the explanation on the list, I could appreciate it ..

The issue it seems for my problem was that while some file copy or say ftp
of a huge file is in progress the memory / pages are used up by prorgrams
already executing and so in the meanwhile if one our  process asks for
memory, it is turned down, we have a very limited memory on board and so
may be thats why I am noticing this kind of behaviour , there is no swap
space either .. after few seconds we can get space for our program, this is
also random in the sense that we can get space while program is running
also , but most of the time we  are turned down saying "out of swap"
So, that's why I was wondering why wasnt it putting  back all the data to
disk (flushing) and less memory shown in top confused me more ..

anyways, I think in my case, limiting the max number of pages for data
buffer caching could be the only way out . using sysctl .. ?
would just decreasing the filemax to a reasonable number do the thing ?
somebody seen like  this and found some way out ?
or am I still on the wrong track . . ?

Thanks for your replies.


"Perry E. Metzger" <> on 03/03/2004 10:11:30

Sent by:

To:    Nitin Mahajan/HSS@HSS

Subject:    Re: swap space for a memory based filesystem writes:
> we are observing that the file copied decreases the top shown free memory

That is totally normal.

> This goes on even if we issue sync command (wasnt it supposed to write
> these dirty pages back to disk ?)

It does, but it keeps the clean pages in memory in case you need to
read them again soon. If the system needs the memory for something
else it will just throw the clean pages away since it doesn't need to
keep them around. There is no unexpected behavior here.