linux-kernel - Re: Freeing page tables through RCU

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Message-ID: <20210226160354.GE2723601@casper.infradead.org>
Date:   Fri, 26 Feb 2021 16:03:54 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Freeing page tables through RCU

On Fri, Feb 26, 2021 at 10:42:00AM -0400, Jason Gunthorpe wrote:
> On Thu, Feb 25, 2021 at 08:58:20PM +0000, Matthew Wilcox wrote:
> 
> > I'd like to hear better ideas than this.
> 
> You didn't like my suggestion to put a sleepable lock around the
> freeing of page tables during flushing?
> 
> I still don't see how you convert the sleepable page walkers to use
> rcu??

I don't want to convert the sleepable ones to use RCU ... I want to
convert the non-sleeping ones to use RCU.  A page_table_free_lock might
work, but it might have its own problems later (eg a sleeping lock can't
be acquired under RCU or spinlock, and it can't be a spinlock because
it'd have to be held while we wait for IPIs).

I think it would solve my immediate problem, and I wonder if it might
solve some other problems ...