On 01/07/2014 03:43 AM, Andrew Morton wrote:
On Mon, 6 Jan 2014 15:51:55 +0530 Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx> wrote:
+ /*
+ * Readahead onto remote memory is better than no readahead when local
+ * numa node does not have memory. We sanitize readahead size depending
+ * on free memory in the local node but limiting to 4k pages.
+ */
+ return local_free_page ? min(sane_nr, local_free_page / 2) : sane_nr;
}
So if the local node has two free pages, we do just one page of
readahead.
Then the local node has one free page and we do zero pages readahead.
Assuming that bug(!) is fixed, the local node now has zero free pages
and we suddenly resume doing large readahead.
This transition from large readahead to very small readahead then back
to large readahead is illogical, surely?
Hi Andrew, Thanks for having a look at this.
You are correct that there is a transition from small readahead to
large once we have zero free pages.
I am not sure I can defend well, but 'll give a try :).
Hoping that we have evenly distributed cpu/memory load, if we have very
less free+inactive memory may be we are in really bad shape already.
But in the case where we have a situation like below [1] (cpu does not
have any local memory node populated) I had mentioned
earlier where we will have to depend on remote node always,
is it not that sanitized readahead onto remote memory seems better?
But having said that I am not able to get an idea of sane implementation
to solve this readahead failure bug overcoming the anomaly you pointed
:(. hints/ideas.. ?? please let me know.
[1]: IBM P730
----------------------------------
# numactl -H
available: 2 nodes (0-1)
node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
23 24 25 26 27 28 29 30 31
node 0 size: 0 MB
node 0 free: 0 MB
node 1 cpus:
node 1 size: 12288 MB
node 1 free: 10440 MB
node distances:
node 0 1
0: 10 40
1: 40 10
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