Re: TMPFS over NFSv4

[Hugh Dickins <hughd@google.com>]

On Mon, May 24, 2010 at 2:26 AM, Tharindu Rukshan Bamunuarachchi
<btharindu@gmail.com> wrote:
> thankx a lot Hugh ... I will try this out ... (bit harder patch
> already patched SLES kernel :-p ) ....

If patch conflicts are a problem, you really only need to put in the
two-liner patch to mm/mmap.c: Alan was seeking perfection in
the rest of the patch, but you can get away without it.

>
> BTW, what does Alan means by "strict overcommit" ?

Ah, that phrase, yes, it's a nonsense, but many of us do say it by mistake.
Alan meant to say "strict no-overcommit".

>
> e.g.
> i did not see this issues with "0 > /proc/sys/vm/overcommit_accounting"

I assume "overcommit_accounting" is either a typo for "overcommit_memory",
or SLES gives "overcommit_memory" a slightly different name.

0 means overcommit memory (let people allocate more private writable user
memory than there is actually ram+swap to back), but throw in a check against
really wild allocation requests.  1 omits even that check.

> But this happened several times with "2 > /proc/sys/vm/overcommit_accounting"

2 means account for all private writable memory and fail any allocation which
would take the system over the edge - the edge being defined roughly by
overcommit_ratio * (ram+swap)  (I expect there's a divisor needed in there!)
i.e. 2 means strict no-overcommit.

So what you see fits with what Alan was fixing.

Hugh