Re: [PATCH] mem notifications v2

["Daniel Spång" <daniel.spang@gmail.com>]

On 11/22/07, Rik van Riel <riel@redhat.com> wrote:
> On Thu, 22 Nov 2007 12:23:55 +0100
> "Daniel Spang" <daniel.spang@gmail.com> wrote:
>
> > When the page cache is filled, the notification is a bit early as the
> > following example shows on a small system with 64 MB ram and no swap.
> > On the first run the application can use 58 MB of anonymous pages
> > before notification is sent. Then after the page cache is filled the
> > test application is runned again and is only able to use 49 MB before
> > being notified.
>
> Excellent.  Throwing away useless memory when three is still
> useful memory available sounds like a good idea.
>
> > I see it as a feature to be able to throw out inactive binaries and
> > mmaped files before getting notified about low memory.
>
> I think that once you get low on memory, you want a bit of
> both.  Inactive binaries and mmaped files are potentially
> useful; in-process free()d memory and caches are just as
> potentially (dubiously) useful.
>
> Freeing a bit of both will probably provide a good compromise
> between CPU and memory efficiency.

I get your point, but strictly speaking, it is never freeing inactive
binaries nor mapped files until all in-process cache are freed. But
your argument is still valid, although a tad weaker, if you replace
``inactive binaries and mmaped files'' with ``page cache''.

> > I suggest we add both this notification and my priority threshold
> > based approach, then the users can chose which one to use.
>
> That sounds like a horribly bad idea, because we run the
> danger of ending up with two sets of applications, both of
> which expect another notification type.
>
> One type of application can cause the other to receive
> unfair amounts of memory pressure.

Sorry, I was a bit vague. I meant using two separate devices and that
the programmer could chose which one to use, based on the importance
of the in-process cache and hopefully decide if it is more valuable
than inactive binaries mmaped files and, to some extent, page cache.

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