From: David Miller <davem@davemloft.net>
To: akpm@linux-foundation.org
Cc: aneesh.kumar@linux.vnet.ibm.com, steve.capper@linaro.org,
aarcange@redhat.com, benh@kernel.crashing.org,
mpe@ellerman.id.au, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-arch@vger.kernel.org, hannes@cmpxchg.org
Subject: Re: [PATCH V2 1/2] mm: Update generic gup implementation to handle hugepage directory
Date: Thu, 23 Oct 2014 18:40:35 -0400 (EDT) [thread overview]
Message-ID: <20141023.184035.388557314666522484.davem@davemloft.net> (raw)
In-Reply-To: <20141022160224.9c2268795e55d5a2eff5b94d@linux-foundation.org>
Hey guys, was looking over the generic GUP while working on a sparc64
issue and I noticed that you guys do speculative page gets, and after
talking with Johannes Weiner (CC:'d) about this we don't see how it
could be necessary.
If interrupts are disabled during the page table scan (which they
are), no IPI tlb flushes can arrive. Therefore any removal from the
page tables is guarded by interrupts being re-enabled. And as a
result, page counts of pages we see in the page tables must always
have a count > 0.
x86 does direct atomic_add() on &page->_count because of this
invariant and I would rather see the generic version do this too.
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next prev parent reply other threads:[~2014-10-23 22:40 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-17 4:38 [PATCH V2 1/2] mm: Update generic gup implementation to handle hugepage directory Aneesh Kumar K.V
2014-10-17 4:38 ` [PATCH V2 2/2] arch/powerpc: Switch to generic RCU get_user_pages_fast Aneesh Kumar K.V
2014-10-17 14:10 ` [PATCH V2 1/2] mm: Update generic gup implementation to handle hugepage directory Steve Capper
2014-10-22 23:02 ` Andrew Morton
2014-10-23 4:28 ` Aneesh Kumar K.V
2014-10-23 8:08 ` Aneesh Kumar K.V
2014-10-23 22:40 ` David Miller [this message]
2014-10-23 23:40 ` Benjamin Herrenschmidt
2014-10-24 3:55 ` David Miller
2014-10-24 8:33 ` Steve Capper
2014-10-24 16:22 ` James Bottomley
2014-10-26 20:50 ` Benjamin Herrenschmidt
2014-10-27 0:18 ` Andrea Arcangeli
2014-10-27 17:58 ` Aneesh Kumar K.V
2014-10-27 18:41 ` Andrea Arcangeli
2014-10-25 10:30 ` Aneesh Kumar K.V
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