Re: [PATCH v2] mm/compaction : do optimazition when the migration scanner gets no page

[Huang Shijie <b32955@freescale.com>]

> On Fri, Jan 13, 2012 at 10:35:42AM +0800, Huang Shijie wrote:
>> Hi,
>>> I think simple patch is returning "return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;"
>>> It's very clear and readable, I think.
>>> In this patch, what's the problem you think?
>>>
>> sorry for the wrong thread, please read the following thread:
>> http://marc.info/?l=linux-mm&m=132532266130861&w=2
> Huang, Thanks for notice that thread.
> I read and if I understand correctly, the point is that Mel want to see tracepoint
> "trace_mm_compaction_migratepages" and account "count_vm_event(COMPACTBLOCKS);"
> My patch does accounting COMPACTBLOCKS so it's not a problem.
Your patch also accounts the COMPACTBLOCKS In the ISOLATE_NONE and 
ISOLATE_ABOART when :
++++++++++++++++++++++++++++++++++++++++++++++++++++++
     /* Do not cross the free scanner or scan within a memory hole */
     if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
         cc->migrate_pfn = end_pfn;
         return ISOLATE_NONE;
     }

     /*
      * Ensure that there are not too many pages isolated from the LRU
      * list by either parallel reclaimers or compaction. If there are,
      * delay for some time until fewer pages are isolated
      */
     while (unlikely(too_many_isolated(zone))) {
         /* async migration should just abort */
         if (!cc->sync)
             return ISOLATE_ABORT;

         congestion_wait(BLK_RW_ASYNC, HZ/10);

         if (fatal_signal_pending(current))
             return ISOLATE_ABORT;
     }
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

this not make sense.
> The problem is my patch doesn't emit trace of "trace_mm_compaction_migratepages".
> But doesn't it matter? When we doesn't isolate any page at all, both argument in
> trace_mm_compaction_migratepages are always zero. Is it meaningful tracepoint?
> Do we really want it?
>
IMHO, yes.

For it _DOES_  scan one PAGEBLOCK even we can not get any page from this 
pageblock.
it should trace the scan even the parameters are both zero.

Huang Shijie
>> Best Regards
>> Huang Shijie
>>


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