From: Matthew Wilcox <willy@infradead.org>
To: Jan Kara <jack@suse.cz>
Cc: "Chris Wilson" <chris@chris-wilson.co.uk>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
intel-gfx@lists.freedesktop.org,
"Andrew Morton" <akpm@linux-foundation.org>,
"Jérôme Glisse" <jglisse@redhat.com>,
"John Hubbard" <jhubbard@nvidia.com>,
"Claudio Imbrenda" <imbrenda@linux.ibm.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
"Jason Gunthorpe" <jgg@ziepe.ca>
Subject: Re: [PATCH] mm: Skip opportunistic reclaim for dma pinned pages
Date: Thu, 25 Jun 2020 17:05:22 +0100 [thread overview]
Message-ID: <20200625160522.GD7703@casper.infradead.org> (raw)
In-Reply-To: <20200625134044.GD17788@quack2.suse.cz>
On Thu, Jun 25, 2020 at 03:40:44PM +0200, Jan Kara wrote:
> On Thu 25-06-20 12:42:09, Matthew Wilcox wrote:
> > Why are DMA pinned pages still on the LRU list at all? I never got an
> > answer to this that made sense to me. By definition, a page which is
> > pinned for DMA is being accessed, and needs to at the very least change
> > position on the LRU list, so just take it off the list when DMA-pinned
> > and put it back on the list when DMA-unpinned.
>
> Well, we do mark_page_accessed() when pinning in GUP. This is not perfect
> but it's as good as it gets with CPU having no control when the page is
> actually accessed. Also taking the page off and then back to LRU list would
> increase the contention on the LRU list locks and generally cost
> performance so for short term pins it is not desirable... Otherwise I agree
> that conceptually it would make some sence although I'm not sure some
> places wouldn't get confused by e.g. page cache pages not being on LRU
> list.
We could/should do what we do for mlocked pages:
Documentation/vm/unevictable-lru.rst
I think 'case five' is wrong and needs to be removed. Pinning is
inappropriate for "I'm going to modify the page myself".
next prev parent reply other threads:[~2020-06-25 16:11 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-24 19:14 [PATCH] mm: Skip opportunistic reclaim for dma pinned pages Chris Wilson
2020-06-24 19:21 ` Jason Gunthorpe
2020-06-24 20:23 ` Yang Shi
2020-06-24 21:02 ` Yang Shi
2020-06-24 20:23 ` Chris Wilson
2020-06-24 20:47 ` John Hubbard
2020-06-24 23:20 ` Jason Gunthorpe
2020-06-25 0:11 ` John Hubbard
2020-06-25 11:24 ` Jan Kara
2020-06-25 7:57 ` Michal Hocko
2020-06-25 11:00 ` Chris Wilson
2020-06-25 15:12 ` Michal Hocko
2020-06-25 15:48 ` Chris Wilson
2020-06-25 11:42 ` Matthew Wilcox
2020-06-25 13:40 ` Jan Kara
2020-06-25 16:05 ` Matthew Wilcox [this message]
2020-06-25 16:32 ` Yang Shi
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