Re: [RFC PATCH V5] mm readahead: Fix readahead fail for no local memory and limit readahead pages

[Raghavendra K T]

On 02/11/2014 03:05 AM, David Rientjes wrote:
> On Mon, 10 Feb 2014, Raghavendra K T wrote:
>
> > So I understood that you are suggesting implementations like below
> >
> > 1) I do not have problem with the below approach, I could post this in
> > next version.
> > ( But this did not include 4k limit Linus mentioned to apply)
> >
> > unsigned long max_sane_readahead(unsigned long nr)
> > {
> >          unsigned long local_free_page;
> >          int nid;
> >
> >          nid = numa_mem_id();
> >
> >          /*
> >           * We sanitize readahead size depending on free memory in
> >           * the local node.
> >           */
> >          local_free_page = node_page_state(nid, NR_INACTIVE_FILE)
> >                            + node_page_state(nid, NR_FREE_PAGES);
> >          return min(nr, local_free_page / 2);
> > }
> >
> > 2) I did not go for below because Honza (Jan Kara) had some
> > concerns for 4k limit for normal case, and since I am not
> > the expert, I was waiting for opinions.
> >
> > unsigned long max_sane_readahead(unsigned long nr)
> > {
> >          unsigned long local_free_page, sane_nr;
> >          int nid;
> >
> >          nid = numa_mem_id();
> > 	/* limit the max readahead to 4k pages */
> > 	sane_nr = min(nr, MAX_REMOTE_READAHEAD);
> >
> >          /*
> >           * We sanitize readahead size depending on free memory in
> >           * the local node.
> >           */
> >          local_free_page = node_page_state(nid, NR_INACTIVE_FILE)
> >                            + node_page_state(nid, NR_FREE_PAGES);
> >          return min(sane_nr, local_free_page / 2);
> > }
>
> I have no opinion on the 4KB pages, either of the above is just fine.

I was able to test (1) implementation on the system where readahead 
problem occurred. Unfortunately it did not help.

Reason seem to be that CONFIG_HAVE_MEMORYLESS_NODES dependency of
numa_mem_id(). The PPC machine I am facing problem has topology like
this:

numactl -H
---------
available: 2 nodes (0-1)
node 0 cpus: 0 1 2 3 4 5 6 7 12 13 14 15 16 17 18 19 20 21 22 23 24 25
...
node 0 size: 0 MB
node 0 free: 0 MB
node 1 cpus: 8 9 10 11 32 33 34 35 ...
node 1 size: 8071 MB
node 1 free: 2479 MB
node distances:
node   0   1
  0:  10  20
  1:  20  10

So it seems numa_mem_id() does not help for all the configs..
Am I missing something ?

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