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Date:   Fri, 16 Aug 2019 10:27:38 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Daniel Vetter <daniel@ffwll.ch>
Cc:     Jason Gunthorpe <jgg@ziepe.ca>, Feng Tang <feng.tang@intel.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Kees Cook <keescook@chromium.org>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
        Jann Horn <jannh@google.com>,
        LKML <linux-kernel@vger.kernel.org>,
        DRI Development <dri-devel@lists.freedesktop.org>,
        Linux MM <linux-mm@kvack.org>,
        =?iso-8859-1?B?Suly9G1l?= Glisse <jglisse@redhat.com>,
        Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        David Rientjes <rientjes@google.com>,
        Wei Wang <wvw@google.com>,
        Daniel Vetter <daniel.vetter@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>
Subject: Re: [Intel-gfx] [PATCH 2/5] kernel.h: Add non_block_start/end()
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On Thu 15-08-19 22:16:43, Daniel Vetter wrote:
> On Thu, Aug 15, 2019 at 9:35 PM Michal Hocko <mhocko@kernel.org> wrote:
[...]
> > > The last detail is I'm still unclear what a GFP flags a blockable
> > > invalidate_range_start() should use. Is GFP_KERNEL OK?
> >
> > I hope I will not make this muddy again ;)
> > invalidate_range_start in the blockable mode can use/depend on any sleepable
> > allocation allowed in the context it is called from. So in other words
> > it is no different from any other function in the kernel that calls into
> > allocator. As the API is missing gfp context then I hope it is not
> > called from any restricted contexts (except from the oom which we have
> > !blockable for).
> 
> Hm, that's new to me. I thought mmu notifiers very much can be called
> from direct reclaim paths, so you have to be extremely careful with
> getting back into that one.

Correct, I should have added that notifier callbacks ideally do not
allocate any memory. They can block and even that is quite a pain to be
honest.
-- 
Michal Hocko
SUSE Labs