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Date: Wed, 30 Dec 2015 12:10:12 -0800
Message-ID: <CA+55aFx0WxoUPrOPaq3HxM+YUQQ0DPV-c3f8kE1ec7agERb_Lg@mail.gmail.com>
Subject: Re: [PATCH v4.4-rc7] sched: isolate task_struct bitfields according
 to synchronization domains
From: Linus Torvalds <torvalds@linux-foundation.org>
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To: Tejun Heo <tj@kernel.org>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>, Ingo Molnar <mingo@redhat.com>, Sasha Levin <sasha.levin@oracle.com>, Andrew Morton <akpm@linux-foundation.org>, Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@kernel.org>, cgroups <cgroups@vger.kernel.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, Vladimir Davydov <vdavydov@parallels.com>, kernel-team <kernel-team@fb.com>, Dmitry Vyukov <dvyukov@google.com>, Peter Zijlstra <peterz@infradead.org>

On Wed, Dec 30, 2015 at 1:23 AM, Tejun Heo <tj@kernel.org> wrote:
>
> Peter, I took the patch and changed the bitfields to ulong.

I wouldn't expect the unsigned long part to matter, except for the
forced split with

   unsigned long :0;

itself.

Also, quite frankly, since this is basically very close to other
fields that are *not* unsigned longs, I'd really prefer to not
unnecessarily use a 64-bit field for three bits each.

So why not just do it with plain unsigned "int", and then maybe just
intersperse them with the other int-sized fields in that neighborhood.

I'm also wondering if we shouldn't just put the scheduler bits in the
"atomic_flags" thing instead?

                     Linus

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From mboxrd@z Thu Jan  1 00:00:00 1970
From: Linus Torvalds <torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
Subject: Re: [PATCH v4.4-rc7] sched: isolate task_struct bitfields according
 to synchronization domains
Date: Wed, 30 Dec 2015 12:10:12 -0800
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To: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Cc: Andrey Ryabinin <ryabinin.a.a-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Ingo Molnar <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Sasha Levin <sasha.levin-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, Michal Hocko <mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, cgroups <cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, "linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org" <linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org>, Vladimir Davydov <vdavydov-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>, kernel-team <kernel-team-b10kYP2dOMg@public.gmane.org>, Dmitry Vyukov <dvyukov-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>

On Wed, Dec 30, 2015 at 1:23 AM, Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> wrote:
>
> Peter, I took the patch and changed the bitfields to ulong.

I wouldn't expect the unsigned long part to matter, except for the
forced split with

   unsigned long :0;

itself.

Also, quite frankly, since this is basically very close to other
fields that are *not* unsigned longs, I'd really prefer to not
unnecessarily use a 64-bit field for three bits each.

So why not just do it with plain unsigned "int", and then maybe just
intersperse them with the other int-sized fields in that neighborhood.

I'm also wondering if we shouldn't just put the scheduler bits in the
"atomic_flags" thing instead?

                     Linus