linux-kernel - Re: [PATCH v5 04/14] mm/gup: check for isolation errors

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Date:   Tue, 19 Jan 2021 14:22:00 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Pavel Tatashin <pasha.tatashin@...een.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, vbabka@...e.cz, mhocko@...e.com,
        david@...hat.com, osalvador@...e.de, dan.j.williams@...el.com,
        sashal@...nel.org, tyhicks@...ux.microsoft.com,
        iamjoonsoo.kim@....com, mike.kravetz@...cle.com,
        rostedt@...dmis.org, mingo@...hat.com, peterz@...radead.org,
        mgorman@...e.de, willy@...radead.org, rientjes@...gle.com,
        jhubbard@...dia.com, linux-doc@...r.kernel.org,
        ira.weiny@...el.com, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v5 04/14] mm/gup: check for isolation errors

On Mon, Jan 18, 2021 at 11:39:10PM -0500, Pavel Tatashin wrote:
> It is still possible that we pin movable CMA pages if there are isolation
> errors and cma_page_list stays empty when we check again.
> 
> Check for isolation errors, and return success only when there are no
> isolation errors, and cma_page_list is empty after checking.
> 
> Because isolation errors are transient, we retry indefinitely.
> 
> Signed-off-by: Pavel Tatashin <pasha.tatashin@...een.com>
> ---
>  mm/gup.c | 60 ++++++++++++++++++++++++++++++++------------------------
>  1 file changed, 34 insertions(+), 26 deletions(-)

This should have a fixme too, this is a bug.

The patch looks OK, but I keep feeling this logic is all really
overcomplicated...

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason