linux-kernel - Re: [PATCH 4/6] mm: introduce page->dma_pinned_flags,

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Message-ID: <2367ff26-809c-da94-a8f0-e921bdc4862a@nvidia.com>
Date:   Wed, 17 Oct 2018 17:03:03 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Michal Hocko <mhocko@...nel.org>
CC:     Jan Kara <jack@...e.cz>, Dave Chinner <david@...morbit.com>,
        Matthew Wilcox <willy@...radead.org>,
        Christopher Lameter <cl@...ux.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Dan Williams <dan.j.williams@...el.com>, <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-rdma <linux-rdma@...r.kernel.org>,
        <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 4/6] mm: introduce page->dma_pinned_flags, _count

On 10/17/18 4:09 AM, Michal Hocko wrote:
> On Tue 16-10-18 18:48:23, John Hubbard wrote:
> [...]
>> It's hard to say exactly what the active/inactive/unevictable list should
>> be when DMA is done and put_user_page*() is called, because we don't know
>> if some device read, wrote, or ignored any of those pages. Although if 
>> put_user_pages_dirty() is called, that's an argument for "active", at least.
> 
> Any reason to not use putback_lru_page?

That does help with which LRU to use. I guess I'd still need to track whether
a page was on an LRU when get_user_pages() was called, because it seems
that that is not necessarily always the case. And putback_lru_page() definitely
wants to deal with a page that *was* previously on an LRU.

> 
> Please note I haven't really got through your patches to have a wider
> picture of the change so this is just hint for the LRU part of the
> issue.
> 

Understood, and the hints are much appreciated.

-- 
thanks,
John Hubbard
NVIDIA