Re: [LSF/MM TOPIC ][LSF/MM ATTEND] Read-only Mapping of Program Text using Large THP Pages

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> On Feb 20, 2019, at 6:44 AM, Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
> 
> That interface would need to have some hint from the VFS as to what
> range of file offsets it's looking for, and which page is the critical
> one.  Maybe that's as simple as passing in pgoff and order, where pgoff is
> not necessarily aligned to 1<<order.  Or maybe we want to explicitly
> pass in start, end, critical.

The order is especially important, as I think it's vital that the FS can
tell the difference between a caller wanting 2M in PAGESIZE pages
(something that could be satisfied by taking multiple trips through the
existing readahead) or needing to transfer ALL the content for a 2M page
as the fault can't be satisfied until the operation is complete. It also
won't be long before reading 1G at a time to map PUD-sized pages becomes
more important, plus the need to support various sizes in-between for
architectures like ARM that support them (see the non-standard size THP
discussion for more on that.)

I'm also hoping the conference would have enough "mixer" time that MM folks
can have a nice discussion with the FS folks to get their input - or at the
very least these mail threads will get that ball rolling.




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