linux-kernel - Re: [PATCH 4/7] mm: defer vmalloc from atomic context

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Date:   Mon, 7 Nov 2016 16:09:47 +0100
From:   Christoph Hellwig <hch@....de>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:     Joel Fernandes <joelaf@...gle.com>, Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jisheng Zhang <jszhang@...vell.com>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        John Dias <joaodias@...gle.com>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        linux-rt-users@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH 4/7] mm: defer vmalloc from atomic context

On Mon, Nov 07, 2016 at 06:01:45PM +0300, Andrey Ryabinin wrote:
> > So because in_atomic doesn't work for !CONFIG_PREEMPT kernels, can we
> > always defer the work in these cases?
> > 
> > So for non-preemptible kernels, we always defer:
> > 
> > if (!IS_ENABLED(CONFIG_PREEMPT) || in_atomic()) {
> >   // defer
> > }
> > 
> > Is this fine? Or any other ideas?
> > 
> 
> What's wrong with my idea?
> We can add vfree_in_atomic() and use it to free vmapped stacks
> and for any other places where vfree() used 'in_atomict() && !in_interrupt()' context.

I somehow missed the mail, sorry.  That beeing said always defer is
going to suck badly in terms of performance, so I'm not sure it's an all
that good idea.

vfree_in_atomic sounds good, but I wonder if we'll need to annotate
more callers than just the stacks.  I'm fairly bust this week, do you
want to give that a spin?  Otherwise I'll give it a try towards the
end of this week or next week.