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Re: [Qemu-devel] [PATCH 04/17] mm: gup: make get_user_pages_fast and __g
From: |
Linus Torvalds |
Subject: |
Re: [Qemu-devel] [PATCH 04/17] mm: gup: make get_user_pages_fast and __get_user_pages_fast latency conscious |
Date: |
Fri, 3 Oct 2014 11:23:53 -0700 |
On Fri, Oct 3, 2014 at 10:07 AM, Andrea Arcangeli <address@hidden> wrote:
> This teaches gup_fast and __gup_fast to re-enable irqs and
> cond_resched() if possible every BATCH_PAGES.
This is disgusting.
Many (most?) __gup_fast() users just want a single page, and the
stupid overhead of the multi-page version is already unnecessary.
This just makes things much worse.
Quite frankly, we should make a single-page version of __gup_fast(),
and convert existign users to use that. After that, the few multi-page
users could have this extra latency control stuff.
And yes, the single-page version of get_user_pages_fast() is actually
latency-critical. shared futexes hit it hard, and yes, I've seen this
in profiles.
Linus
- [Qemu-devel] [PATCH 00/17] RFC: userfault v2, Andrea Arcangeli, 2014/10/03
- [Qemu-devel] [PATCH 03/17] mm: gup: use get_user_pages_unlocked within get_user_pages_fast, Andrea Arcangeli, 2014/10/03
- [Qemu-devel] [PATCH 16/17] powerpc: add remap_anon_pages and userfaultfd, Andrea Arcangeli, 2014/10/03
- [Qemu-devel] [PATCH 14/17] userfaultfd: add new syscall to provide memory externalization, Andrea Arcangeli, 2014/10/03
- [Qemu-devel] [PATCH 01/17] mm: gup: add FOLL_TRIED, Andrea Arcangeli, 2014/10/03
- [Qemu-devel] [PATCH 06/17] kvm: Faults which trigger IO release the mmap_sem, Andrea Arcangeli, 2014/10/03
- [Qemu-devel] [PATCH 04/17] mm: gup: make get_user_pages_fast and __get_user_pages_fast latency conscious, Andrea Arcangeli, 2014/10/03
- Re: [Qemu-devel] [PATCH 04/17] mm: gup: make get_user_pages_fast and __get_user_pages_fast latency conscious,
Linus Torvalds <=
- [Qemu-devel] [PATCH 11/17] mm: swp_entry_swapcount, Andrea Arcangeli, 2014/10/03
- [Qemu-devel] [PATCH 15/17] userfaultfd: make userfaultfd_write non blocking, Andrea Arcangeli, 2014/10/03
- [Qemu-devel] [PATCH 13/17] waitqueue: add nr wake parameter to __wake_up_locked_key, Andrea Arcangeli, 2014/10/03
- [Qemu-devel] [PATCH 09/17] mm: PT lock: export double_pt_lock/unlock, Andrea Arcangeli, 2014/10/03
- [Qemu-devel] [PATCH 07/17] mm: madvise MADV_USERFAULT: prepare vm_flags to allow more than 32bits, Andrea Arcangeli, 2014/10/03
- [Qemu-devel] [PATCH 10/17] mm: rmap preparation for remap_anon_pages, Andrea Arcangeli, 2014/10/03