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

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Message-ID: <20181019081115.GM18839@dhcp22.suse.cz>
Date:   Fri, 19 Oct 2018 10:11:15 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     John Hubbard <jhubbard@...dia.com>
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 Wed 17-10-18 17:03:03, John Hubbard wrote:
> 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.

Well, if you ever g-u-p pages which are never going to go to LRU then
sure (e.g. hugetlb pages).
-- 
Michal Hocko
SUSE Labs