From: Alistair Popple <apopple@nvidia.com>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: <linux-mm@kvack.org>, <nouveau@lists.freedesktop.org>,
<bskeggs@redhat.com>, <akpm@linux-foundation.org>,
<linux-doc@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
<kvm-ppc@vger.kernel.org>, <dri-devel@lists.freedesktop.org>,
<jhubbard@nvidia.com>, <rcampbell@nvidia.com>,
<jglisse@redhat.com>, <hch@infradead.org>, <daniel@ffwll.ch>,
<willy@infradead.org>, "Christoph Hellwig" <hch@lst.de>
Subject: Re: [PATCH v7 3/8] mm/rmap: Split try_to_munlock from try_to_unmap
Date: Wed, 31 Mar 2021 09:09:30 +1100 [thread overview]
Message-ID: <12442194.rtmf8Ope3M@nvdebian> (raw)
In-Reply-To: <20210330184903.GZ2356281@nvidia.com>
On Wednesday, 31 March 2021 5:49:03 AM AEDT Jason Gunthorpe wrote:
> On Fri, Mar 26, 2021 at 11:08:00AM +1100, Alistair Popple wrote:
>
> > +static bool try_to_munlock_one(struct page *page, struct vm_area_struct
*vma,
> > + unsigned long address, void *arg)
> > +{
>
> Is this function name right?
Perhaps. This is called from try_to_munlock() hence the name, but see below
for some commentary on that naming.
> > + struct page_vma_mapped_walk pvmw = {
> > + .page = page,
> > + .vma = vma,
> > + .address = address,
> > + };
> > +
> > + /* munlock has nothing to gain from examining un-locked vmas */
> > + if (!(vma->vm_flags & VM_LOCKED))
> > + return true;
> > +
> > + while (page_vma_mapped_walk(&pvmw)) {
> > + /* PTE-mapped THP are never mlocked */
> > + if (!PageTransCompound(page)) {
> > + /*
> > + * Holding pte lock, we do *not* need
> > + * mmap_lock here
> > + */
> > + mlock_vma_page(page);
>
> Because the only action this function seems to take is to call
> *mlock*_vma_page()
>
> > + }
> > + page_vma_mapped_walk_done(&pvmw);
> > +
> > + /* found a mlocked page, no point continuing munlock check */
> > + return false;
> > + }
> > +
> > + return true;
> > +}
> > +
> > /**
> > * try_to_munlock - try to munlock a page
> > * @page: the page to be munlocked
> > @@ -1796,8 +1821,7 @@ bool try_to_unmap(struct page *page, enum ttu_flags
flags)
> > void try_to_munlock(struct page *page)
> > {
>
> But this is also called try_to_munlock ??
As far as I can tell this has always been called try_to_munlock() even though
it appears to do the opposite.
> /**
> * try_to_munlock - try to munlock a page
> * @page: the page to be munlocked
> *
> * Called from munlock code. Checks all of the VMAs mapping the page
> * to make sure nobody else has this page mlocked. The page will be
> * returned with PG_mlocked cleared if no other vmas have it mlocked.
> */
In other words it sets PG_mlocked if one or more vmas has it mlocked. So
try_to_mlock() might be a better name, except that seems to have the potential
for confusion as well because it's only called from the munlock code path and
never for mlock.
> So what clears PG_mlocked on this call path?
See munlock_vma_page(). munlock works by clearing PG_mlocked, then calling
try_to_munlock to check if any VMAs still need it locked in which case
PG_mlocked gets set again. There are no other callers of try_to_munlock().
> Something needs attention here..
I think the code is correct, but perhaps the naming could be better. Would be
interested hearing any thoughts on renaming try_to_munlock() to try_to_mlock()
as the current name appears based on the context it is called from (munlock)
rather than what it does (mlock).
- Alistair
> Jason
>
next prev parent reply other threads:[~2021-03-30 22:10 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-26 0:07 [PATCH v7 0/8] Add support for SVM atomics in Nouveau Alistair Popple
2021-03-26 0:07 ` [PATCH v7 1/8] mm: Remove special swap entry functions Alistair Popple
2021-03-30 18:38 ` Jason Gunthorpe
2021-03-26 0:07 ` [PATCH v7 2/8] mm/swapops: Rework swap entry manipulation code Alistair Popple
2021-03-26 0:08 ` [PATCH v7 3/8] mm/rmap: Split try_to_munlock from try_to_unmap Alistair Popple
2021-03-30 18:49 ` Jason Gunthorpe
2021-03-30 22:09 ` Alistair Popple [this message]
2021-03-30 22:16 ` Alistair Popple
2021-03-30 22:24 ` Jason Gunthorpe
2021-03-30 22:43 ` John Hubbard
2021-03-30 22:56 ` Alistair Popple
2021-03-31 3:56 ` John Hubbard
2021-03-31 4:09 ` John Hubbard
2021-03-31 4:15 ` Alistair Popple
2021-03-31 11:57 ` Jason Gunthorpe
2021-04-01 4:36 ` Alistair Popple
2021-04-01 19:21 ` Shakeel Butt
2021-03-26 0:08 ` [PATCH v7 4/8] mm/rmap: Split migration into its own function Alistair Popple
2021-03-26 0:08 ` [PATCH v7 5/8] mm: Device exclusive memory access Alistair Popple
2021-03-30 19:32 ` Jason Gunthorpe
2021-03-31 12:59 ` Alistair Popple
2021-03-31 13:18 ` Jason Gunthorpe
2021-03-31 13:27 ` Alistair Popple
2021-03-31 13:46 ` Jason Gunthorpe
2021-04-01 0:45 ` Alistair Popple
2021-04-01 0:48 ` Jason Gunthorpe
2021-04-01 2:20 ` Alistair Popple
2021-04-01 11:55 ` Jason Gunthorpe
2021-03-26 0:08 ` [PATCH v7 6/8] mm: Selftests for exclusive device memory Alistair Popple
2021-03-26 0:08 ` [PATCH v7 7/8] nouveau/svm: Refactor nouveau_range_fault Alistair Popple
2021-03-26 0:08 ` [PATCH v7 8/8] nouveau/svm: Implement atomic SVM access Alistair Popple
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