Re: [PATCHv6 00/22] Transparent huge page cache: phase 1, everythingbut mmap()

[Dave Hansen]

On 09/30/2013 03:02 AM, Mel Gorman wrote:
> I am afraid I never looked too closely once I learned that the primary
> motivation for this was relieving iTLB pressure in a very specific
> case. AFAIK, this is not a problem in the vast majority of modern CPUs
> and I found it very hard to be motivated to review the series as a result.
> I suspected that in many cases that the cost of IO would continue to dominate
> performance instead of TLB pressure. I also found it unlikely that there
> was a workload that was tmpfs based that used enough memory to be hurt
> by TLB pressure. My feedback was that a much more compelling case for the
> series was needed but this discussion all happened on IRC unfortunately.

FWIW, I'm mostly intrigued by the possibilities of how this can speed up
_software_, and I'm rather uninterested in what it can do for the TLB.
Page cache is particularly painful today, precisely because hugetlbfs
and anonymous-thp aren't available there.  If you have an app with
hundreds of GB of files that it wants to mmap(), even if it's in the
page cache, it takes _minutes_ to just fault in.  One example:

	https://lkml.org/lkml/2013/6/27/698
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