Messages in this thread | | | From | Andreas Gruenbacher <> | Date | Fri, 3 Dec 2021 19:11:58 +0100 | Subject | Re: [PATCH v2 0/4] Avoid live-lock in fault-in+uaccess loops with sub-page faults |
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On Fri, Dec 3, 2021 at 6:58 PM Linus Torvalds <torvalds@linux-foundation.org> wrote: > On Fri, Dec 3, 2021 at 7:29 AM Andreas Gruenbacher <agruenba@redhat.com> wrote: > > We're trying pretty hard to handle large I/O requests efficiently at > > the filesystem level. A small, static upper limit in the fault-in > > functions has the potential to ruin those efforts. So I'm not a fan of > > that. > > I don't think fault-in should happen under any sane normal circumstances. > > Except for low-memory situations, and then you don't want to fault in > large areas. > > Do you really expect to write big areas that the user has never even > touched? That would be literally insane. > > And if the user _has_ touched them, then they'll in in-core. Except > for the "swapped out" case. > > End result: this is purely a correctness issue, not a performance issue.
It happens when you mmap a file and write the mmapped region to another file, for example. I don't think we want to make filesystems go bonkers in such scenarios. Scaling down in response to memory pressure sounds perfectly fine though.
Thanks, Andreas
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