From: Minchan Kim <minchan@kernel.org>
To: John Hubbard <jhubbard@nvidia.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
"Paul E . McKenney" <paulmck@kernel.org>,
John Dias <joaodias@google.com>,
David Hildenbrand <david@redhat.com>
Subject: Re: [PATCH v4] mm: fix is_pinnable_page against on cma page
Date: Wed, 11 May 2022 16:28:02 -0700 [thread overview]
Message-ID: <YnxGgo9iCsnOOBHE@google.com> (raw)
In-Reply-To: <YnxDhdb4YCo19Qx0@google.com>
On Wed, May 11, 2022 at 04:15:17PM -0700, Minchan Kim wrote:
> On Wed, May 11, 2022 at 04:13:10PM -0700, John Hubbard wrote:
> > On 5/11/22 16:08, Minchan Kim wrote:
> > > > OK, so the code checks the wrong item each time. But the code really
> > > > only needs to know "is either _CMA or _ISOLATE set?". And so you
> > >
> > > Yes.
> > >
> > > > can just sidestep the entire question by writing it like this:
> > > >
> > > > int mt = get_pageblock_migratetype(page);
> > > >
> > > > if (mt & (MIGRATE_ISOLATE | MIGRATE_CMA))
> > > > return false;
> > >
> > > I am confused. Isn't it same question?
> > >
> > > set_pageblock_migratetype(MIGRATE_ISOLATE)
> > > if (get_pageblock_migrate(page) & MIGRATE_CMA)
> > >
> > > set_pageblock_migratetype(MIGRATE_CMA)
> > >
> > > if (get_pageblock_migrate(page) & MIGRATE_ISOLATE)
> >
> > Well no, because the "&" operation is a single operation on the CPU, and
> > isn't going to get split up like that.
>
> Oh, if that's true, yeah, I could live with it.
>
> Thanks, let me post next revision with commenting about that.
This is delta to confirm before posting next revision.
Are you okay with this one?
diff --git a/include/linux/mm.h b/include/linux/mm.h
index cbf79eb790e0..7b2df6780552 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1626,14 +1626,14 @@ static inline bool page_needs_cow_for_dma(struct vm_area_struct *vma,
static inline bool is_pinnable_page(struct page *page)
{
#ifdef CONFIG_CMA
+ int mt = get_pageblock_migratetype(page);
+
/*
- * use volatile to use local variable mt instead of
- * refetching mt value.
+ * "&" operation would prevent compiler split up
+ * get_pageblock_migratetype two times for each
+ * condition check: refetching mt value two times.
*/
- int __mt = get_pageblock_migratetype(page);
- int mt = __READ_ONCE(__mt);
-
- if (mt == MIGRATE_CMA || mt == MIGRATE_ISOLATE)
+ if (mt & (MIGRATE_ISOLATE | MIGRATE_CMA))
return false;
#endif
next prev parent reply other threads:[~2022-05-11 23:28 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-10 21:17 [PATCH v4] mm: fix is_pinnable_page against on cma page Minchan Kim
2022-05-10 22:56 ` John Hubbard
2022-05-10 23:31 ` Minchan Kim
2022-05-10 23:58 ` John Hubbard
2022-05-11 0:09 ` Minchan Kim
2022-05-11 4:32 ` John Hubbard
2022-05-11 21:46 ` Minchan Kim
2022-05-11 22:25 ` John Hubbard
2022-05-11 22:37 ` Minchan Kim
2022-05-11 22:49 ` John Hubbard
2022-05-11 23:08 ` Minchan Kim
2022-05-11 23:13 ` John Hubbard
2022-05-11 23:15 ` Minchan Kim
2022-05-11 23:28 ` Minchan Kim [this message]
2022-05-11 23:33 ` John Hubbard
2022-05-11 23:45 ` Paul E. McKenney
2022-05-11 23:57 ` John Hubbard
2022-05-12 0:12 ` Paul E. McKenney
2022-05-12 0:12 ` John Hubbard
2022-05-12 0:22 ` Paul E. McKenney
2022-05-12 0:26 ` Minchan Kim
2022-05-12 0:34 ` John Hubbard
2022-05-12 0:49 ` Paul E. McKenney
2022-05-12 1:02 ` John Hubbard
2022-05-12 1:03 ` Minchan Kim
2022-05-12 1:08 ` John Hubbard
2022-05-12 2:18 ` John Hubbard
2022-05-12 3:44 ` Minchan Kim
2022-05-12 4:47 ` John Hubbard
2022-05-17 14:00 ` Jason Gunthorpe
2022-05-17 18:12 ` John Hubbard
2022-05-17 19:28 ` Jason Gunthorpe
2022-05-17 20:12 ` John Hubbard
2022-05-17 20:21 ` Paul E. McKenney
2022-05-23 16:33 ` Minchan Kim
2022-05-24 2:55 ` John Hubbard
2022-05-24 5:16 ` Minchan Kim
2022-05-24 6:22 ` John Hubbard
2022-05-24 14:19 ` Jason Gunthorpe
2022-05-24 15:43 ` Minchan Kim
2022-05-24 15:48 ` Jason Gunthorpe
2022-05-24 16:37 ` Paul E. McKenney
2022-05-24 16:59 ` Minchan Kim
2022-05-12 3:57 ` Paul E. McKenney
2022-05-12 1:03 ` Minchan Kim
2022-05-12 0:35 ` Paul E. McKenney
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