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SubjectRe: [patch v2 1/2] mm, mmu_notifier: annotate mmu notifiers with blockable invalidate callbacks
On Fri 15-12-17 15:04:29, Andrew Morton wrote:
> On Thu, 14 Dec 2017 13:30:56 -0800 (PST) David Rientjes <rientjes@google.com> wrote:
>
> > Commit 4d4bbd8526a8 ("mm, oom_reaper: skip mm structs with mmu notifiers")
> > prevented the oom reaper from unmapping private anonymous memory with the
> > oom reaper when the oom victim mm had mmu notifiers registered.
> >
> > The rationale is that doing mmu_notifier_invalidate_range_{start,end}()
> > around the unmap_page_range(), which is needed, can block and the oom
> > killer will stall forever waiting for the victim to exit, which may not
> > be possible without reaping.
> >
> > That concern is real, but only true for mmu notifiers that have blockable
> > invalidate_range_{start,end}() callbacks. This patch adds a "flags" field
> > to mmu notifier ops that can set a bit to indicate that these callbacks do
> > not block.
> >
> > The implementation is steered toward an expensive slowpath, such as after
> > the oom reaper has grabbed mm->mmap_sem of a still alive oom victim.
>
> some tweakage, please review.
>
> From: Andrew Morton <akpm@linux-foundation.org>
> Subject: mm-mmu_notifier-annotate-mmu-notifiers-with-blockable-invalidate-callbacks-fix
>
> make mm_has_blockable_invalidate_notifiers() return bool, use rwsem_is_locked()

Yes, that makes sense to me.

>
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Cc: Andrea Arcangeli <aarcange@redhat.com>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Cc: Christian König <christian.koenig@amd.com>
> Cc: David Airlie <airlied@linux.ie>
> Cc: David Rientjes <rientjes@google.com>
> Cc: Dimitri Sivanich <sivanich@hpe.com>
> Cc: Doug Ledford <dledford@redhat.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Jérôme Glisse <jglisse@redhat.com>
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Mike Marciniszyn <mike.marciniszyn@intel.com>
> Cc: Oded Gabbay <oded.gabbay@gmail.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Cc: Sean Hefty <sean.hefty@intel.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
>
> include/linux/mmu_notifier.h | 7 ++++---
> mm/mmu_notifier.c | 8 ++++----
> 2 files changed, 8 insertions(+), 7 deletions(-)
>
> diff -puN include/linux/mmu_notifier.h~mm-mmu_notifier-annotate-mmu-notifiers-with-blockable-invalidate-callbacks-fix include/linux/mmu_notifier.h
> --- a/include/linux/mmu_notifier.h~mm-mmu_notifier-annotate-mmu-notifiers-with-blockable-invalidate-callbacks-fix
> +++ a/include/linux/mmu_notifier.h
> @@ -2,6 +2,7 @@
> #ifndef _LINUX_MMU_NOTIFIER_H
> #define _LINUX_MMU_NOTIFIER_H
>
> +#include <linux/types.h>
> #include <linux/list.h>
> #include <linux/spinlock.h>
> #include <linux/mm_types.h>
> @@ -233,7 +234,7 @@ extern void __mmu_notifier_invalidate_ra
> bool only_end);
> extern void __mmu_notifier_invalidate_range(struct mm_struct *mm,
> unsigned long start, unsigned long end);
> -extern int mm_has_blockable_invalidate_notifiers(struct mm_struct *mm);
> +extern bool mm_has_blockable_invalidate_notifiers(struct mm_struct *mm);
>
> static inline void mmu_notifier_release(struct mm_struct *mm)
> {
> @@ -473,9 +474,9 @@ static inline void mmu_notifier_invalida
> {
> }
>
> -static inline int mm_has_blockable_invalidate_notifiers(struct mm_struct *mm)
> +static inline bool mm_has_blockable_invalidate_notifiers(struct mm_struct *mm)
> {
> - return 0;
> + return false;
> }
>
> static inline void mmu_notifier_mm_init(struct mm_struct *mm)
> diff -puN mm/mmu_notifier.c~mm-mmu_notifier-annotate-mmu-notifiers-with-blockable-invalidate-callbacks-fix mm/mmu_notifier.c
> --- a/mm/mmu_notifier.c~mm-mmu_notifier-annotate-mmu-notifiers-with-blockable-invalidate-callbacks-fix
> +++ a/mm/mmu_notifier.c
> @@ -240,13 +240,13 @@ EXPORT_SYMBOL_GPL(__mmu_notifier_invalid
> * Must be called while holding mm->mmap_sem for either read or write.
> * The result is guaranteed to be valid until mm->mmap_sem is dropped.
> */
> -int mm_has_blockable_invalidate_notifiers(struct mm_struct *mm)
> +bool mm_has_blockable_invalidate_notifiers(struct mm_struct *mm)
> {
> struct mmu_notifier *mn;
> int id;
> - int ret = 0;
> + bool ret = false;
>
> - WARN_ON_ONCE(down_write_trylock(&mm->mmap_sem));
> + WARN_ON_ONCE(!rwsem_is_locked(&mm->mmap_sem));
>
> if (!mm_has_notifiers(mm))
> return ret;
> @@ -259,7 +259,7 @@ int mm_has_blockable_invalidate_notifier
> continue;
>
> if (!(mn->ops->flags & MMU_INVALIDATE_DOES_NOT_BLOCK)) {
> - ret = 1;
> + ret = true;
> break;
> }
> }
> _
>
> --
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--
Michal Hocko
SUSE Labs

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