[Devel] Re: [PATCH 0/8] RSS controller based on process containers (v3.1)

[Herbert Poetzl]

On Mon, Jun 04, 2007 at 05:25:25PM +0400, Pavel Emelianov wrote:
> Adds RSS accounting and control within a container.
> 
> Changes from v3
>  - comments across the code
>  - git-bisect safe split
>  - lost places to move the page between active/inactive lists
> 
> Ported above Paul's containers V10 with fixes from Balbir.
> 
> RSS container includes the per-container RSS accounting
> and reclamation, and out-of-memory killer.
> 
> 
> Each mapped page has an owning container and is linked into its 
> LRU lists just like in the global LRU ones. The owner of the page 
> is the container that touched the page first. 

> As long as the page stays mapped it holds the container, is accounted 
> into its usage and lives in its LRU list. When page is unmapped for   
> the last time it releases the container.                              

> The RSS usage is exactly the number of pages in its booth LRU lists,
> i.e. the nu,ber of pages used by this container.

so there could be two guests, unified (i.e. sharing 
most of the files as hardlinks), where the first one
holds 80% of the resulting pages, and the second one
20%, and thus shows much lower 'RSS' usage as the
other one, although it is running the very same
processes and providing identical services?

> When this usage exceeds the limit set some pages are reclaimed from
> the owning container. In case no reclamation possible the OOM killer
> starts thinning out the container.

so the system (physical machine) starts reclaiming
and probably swapping even when there is no need
to do so?

e.g. a system with a single guest, limited to 10k
pages, with a working set of 15k pages in different
apps would continuously swap (trash?) on an otherwise
unused (100k+ pages) system?

> Thus the container behaves like a standalone machine - when it runs
> out of resources, it tries to reclaim some pages, and if it doesn't
> succeed, kills some task.

is that really what we want?
I think we can do _better_ than a standalone machine
and in many cases we really should ...

best,
Herbert

> Signed-off-by: Pavel Emelianov <xemul at openvz.org>
> 
> The testing scenario may look like this:
> 
> 1. Prepare the containers
> # mkdir -p /containers/rss
> # mount -t container none /containers/rss -o rss
> 
> 2. Make the new group and move bash into it
> # mkdir /containers/rss/0
> # echo $$ >  /containers/rss/0/tasks
> 
> Since now we're in the 0 container.
> We can alter the RSS limit
> # echo -n 6000 > /containers/rss/0/rss_limit
> 
> We can check the usage
> # cat /containers/rss/0/rss_usage 
> 25
> 
> And do other stuff. To check the reclamation to work we need a
> simple program that touches many pages of memory, like this:
> 
> #include <stdio.h>
> #include <unistd.h>
> #include <sys/mman.h>
> #include <fcntl.h>
> 
> #ifndef PGSIZE
> #define PGSIZE  4096
> #endif
> 
> int main(int argc, char **argv)
> {
>         unsigned long pages;
>         int i;
>         char *mem;
> 
>         if (argc < 2) {
>                 printf("Usage: %s <number_of_pages>\n", argv[0]);
>                 return 1;
>         }
> 
>         pages = strtol(argv[1], &mem, 10);
>         if (*mem != '\0') {
>                 printf("Bad number %s\n", argv[1]);
>                 return 1;
>         }
> 
>         mem = mmap(NULL, pages * PGSIZE, PROT_READ | PROT_WRITE,
>                         MAP_PRIVATE | MAP_ANON, 0, 0);
>         if (mem == MAP_FAILED) {
>                 perror("map");
>                 return 2;
>         }
> 
>         for (i = 0; i < pages; i++)
>                 mem[i * PGSIZE] = 0;
> 
>         printf("OK\n");
>         return 0;
> }
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