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SubjectRe: [RFC PATCH 0/6] Add support for shared PTEs across processes
On Tue, Jan 25, 2022 at 09:57:05PM +0300, Kirill A. Shutemov wrote:
> On Tue, Jan 25, 2022 at 02:09:47PM +0000, Matthew Wilcox wrote:
> > > I think zero-API approach (plus madvise() hints to tweak it) is worth
> > > considering.
> >
> > I think the zero-API approach actually misses out on a lot of
> > possibilities that the mshare() approach offers. For example, mshare()
> > allows you to mmap() many small files in the shared region -- you
> > can't do that with zeroAPI.
>
> Do you consider a use-case for many small files to be common? I would
> think that the main consumer of the feature to be mmap of huge files.
> And in this case zero enabling burden on userspace side sounds like a
> sweet deal.

mmap() of huge files is certainly the Oracle use-case. With occasional
funny business like mprotect() of a single page in the middle of a 1GB
hugepage.

The approach of designating ranges of a process's address space as
sharable with other processes felt like the cleaner & frankly more
interesting approach that opens up use-cases other than "hurr, durr, we
are Oracle, we like big files, kernel get out of way now, transactions
to perform".

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