linux-kernel - Re: [PATCH v9 07/10] mm: Device exclusive memory access

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Message-ID: <YLpE0U789jvD2zxN@t490s>
Date:   Fri, 4 Jun 2021 11:20:49 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Alistair Popple <apopple@...dia.com>
Cc:     Balbir Singh <bsingharora@...il.com>,
        John Hubbard <jhubbard@...dia.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        nouveau@...ts.freedesktop.org, bskeggs@...hat.com,
        rcampbell@...dia.com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        hch@...radead.org, jglisse@...hat.com, willy@...radead.org,
        jgg@...dia.com, hughd@...gle.com, Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v9 07/10] mm: Device exclusive memory access

On Fri, Jun 04, 2021 at 11:07:42AM +1000, Alistair Popple wrote:
> On Friday, 4 June 2021 12:47:40 AM AEST Peter Xu wrote:
> > External email: Use caution opening links or attachments
> > 
> > On Thu, Jun 03, 2021 at 09:39:32PM +1000, Alistair Popple wrote:
> > > Reclaim won't run on the page due to the extra references from the special
> > > swap entries.
> > 
> > That sounds reasonable, but I didn't find the point that stops it, probably
> > due to my limited knowledge on the reclaim code.  Could you elaborate?
> 
> Sure, it isn't immediately obvious but it ends up being detected at the start 
> of is_page_cache_freeable() in the pageout code:
> 
> 
> static pageout_t pageout(struct page *page, struct address_space *mapping)
> {
> 
> [...]
> 
> 	if (!is_page_cache_freeable(page))
> 		return PAGE_KEEP;

I did look at pageout() but still missed this small helper indeed (while it's
so important to know..), thanks!

-- 
Peter Xu