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Message-ID: <20161026090705.GA18382@dhcp22.suse.cz>
Date: Wed, 26 Oct 2016 11:07:05 +0200
From: Michal Hocko <mhocko@...nel.org>
To: Lorenzo Stoakes <lstoakes@...il.com>
Cc: linux-mm@...ck.org, Linus Torvalds <torvalds@...ux-foundation.org>,
Jan Kara <jack@...e.cz>, Hugh Dickins <hughd@...gle.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Rik van Riel <riel@...hat.com>,
Mel Gorman <mgorman@...hsingularity.net>,
Andrew Morton <akpm@...ux-foundation.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Radim Krčmář <rkrcmar@...hat.com>,
kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: remove unnecessary __get_user_pages_unlocked() calls
On Wed 26-10-16 08:59:52, Lorenzo Stoakes wrote:
> On Wed, Oct 26, 2016 at 12:36:09AM +0100, Lorenzo Stoakes wrote:
> > In hva_to_pfn_slow() we are able to replace __get_user_pages_unlocked() with
> > get_user_pages_unlocked() since we can now pass gup_flags.
> >
> > In async_pf_execute() we need to pass different tsk, mm arguments so
> > get_user_pages_remote() is the sane replacement here (having added manual
> > acquisition and release of mmap_sem.)
> >
> > Since we pass a NULL pages parameter the subsequent call to
> > __get_user_pages_locked() will have previously bailed any attempt at
> > VM_FAULT_RETRY, so we do not change this behaviour by using
> > get_user_pages_remote() which does not invoke VM_FAULT_RETRY logic at all.
> >
> > Signed-off-by: Lorenzo Stoakes <lstoakes@...il.com>
>
> Note that the use of get_user_pages_remote() in async_pf_execute() reintroduces
> the use of the FOLL_TOUCH flag - I don't think this is a problem as this flag
> was dropped by 1e987790 ("mm/gup: Introduce get_user_pages_remote()") which
> states 'Without protection keys, this patch should not change any behavior', so
> I don't think this was intentional.
Yes, I have already mentioned this in one of my previous emails. This
indeed doesn't seem to be intentional
--
Michal Hocko
SUSE Labs
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