Re: Populating multiple ptes at fault time

["Martin Bligh" <mbligh@mbligh.org>]

>>> My patches were only for anonymous pages not for file backed because readahead
>>> is available for file backed mappings.
>>
>> Do we populate the PTEs though? I didn't think that was batched, but I
>> might well be wrong.
>
> We do not populate the PTEs and AFAICT PTE population was assumed not to be
> performance critical since the backing media is comparatively slow.

I think the times when this matters are things like glibc, which are
heavily shared -
we were only 'prefaulting' when the pagecache was already there. So it's a case
for a "readahead like algorithm", not necessarily a direct hook.

Anonymous pages seem much riskier, as presumably there's a no backing page
except in the fork case.

I presume the reason Jeremy is interested is because his pagefaults are more
expensive than most (under virtualization), so he may well find a
different tradeoff
than I did (try running kernbench?)

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