linux-kernel - Re: [PATCH 1/4] mm: Trial do_wp

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Message-ID: <20200914143829.GA1424636@nvidia.com>
Date:   Mon, 14 Sep 2020 11:38:29 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Peter Xu <peterx@...hat.com>, Leon Romanovsky <leonro@...dia.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        "Maya B . Gokhale" <gokhale2@...l.gov>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Marty Mcfadden <mcfadden8@...l.gov>,
        Kirill Shutemov <kirill@...temov.name>,
        Oleg Nesterov <oleg@...hat.com>, Jann Horn <jannh@...gle.com>,
        Jan Kara <jack@...e.cz>, Kirill Tkhai <ktkhai@...tuozzo.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/4] mm: Trial do_wp_page() simplification

On Fri, Aug 21, 2020 at 07:49:55PM -0400, Peter Xu wrote:
> From: Linus Torvalds <torvalds@...ux-foundation.org>
> 
> How about we just make sure we're the only possible valid user fo the
> page before we bother to reuse it?
> 
> Simplify, simplify, simplify.
> 
> And get rid of the nasty serialization on the page lock at the same time.
> 
> Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
> [peterx: add subject prefix]
> Signed-off-by: Peter Xu <peterx@...hat.com>
>  mm/memory.c | 59 +++++++++++++++--------------------------------------
>  1 file changed, 17 insertions(+), 42 deletions(-)

I don't have a detailed explanation right now, but this patch appears
to be causing a regression where RDMA subsystem tests fail. Tests
return to normal when this patch is reverted.

It kind of looks like the process is not seeing DMA'd data to a
pin_user_pages()?

Thanks,
Jason