On 10/11/2011 04:54 PM, Andrew Morton wrote:
On Tue, 11 Oct 2011 16:23:22 -0400
Satoru Moriya<satoru.moriya@xxxxxxx> wrote:
On 10/11/2011 03:55 PM, Andrew Morton wrote:
On Tue, 11 Oct 2011 15:32:11 -0400
Satoru Moriya<satoru.moriya@xxxxxxx> wrote:
On 10/10/2011 06:37 PM, Andrew Morton wrote:
On Fri, 7 Oct 2011 20:08:19 -0700 (PDT) David Rientjes
<rientjes@xxxxxxxxxx> wrote:
On Thu, 1 Sep 2011, Rik van Riel wrote:
Actually page allocator decreases min watermark to 3/4 * min
watermark for rt-task. But in our case some applications create a lot
of processes and if all of them are rt-task, the amount of watermark
bonus(1/4 * min watermark) is not enough.
If we can tune the amount of bonus, it may be fine. But that is
almost all same as extra free kbytes.
This situation is detectable at runtime. If realtime tasks are being
stalled in the page allocator then start to increase the free-page
reserves. A little control system.
Detecting at runtime is too late for some latency critical systems.
At that system, we must avoid a stall before it happens.
It's pretty darn obvious that the kernel can easily see the situation
developing before it happens. By comparing a few integers.
The problem is that we may be dealing with bursts, not steady
states of allocations. Without knowing the size of a burst,
we have no idea when we should wake up kswapd to get enough
memory freed ahead of the application's allocations.
Look, please don't go bending over backwards like this to defend a bad
patch. It's a bad patch! It would be better not to have to merge it.
Let's do something better.
I would love it if we could come up with something better,
and have thought about it a lot.
However, so far we do not seem to have an alternative yet :(
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