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From: Michal Hocko <mhocko@kernel.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>,
	penguin-kernel@I-love.SAKURA.ne.jp, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, hpa@zytor.com, chris@chris-wilson.co.uk,
	hch@lst.de, mingo@elte.hu, jszhang@marvell.com,
	joelaf@google.com, joaodias@google.com, willy@infradead.org,
	tglx@linutronix.de, thellstrom@vmware.com,
	stable@vger.kernel.org
Subject: Re: [PATCH 1/4] mm/vmalloc: allow to call vfree() in atomic context
Date: Tue, 4 Apr 2017 11:36:53 +0200	[thread overview]
Message-ID: <20170404093653.GG15132@dhcp22.suse.cz> (raw)
In-Reply-To: <20170330152229.f2108e718114ed77acae7405@linux-foundation.org>

On Thu 30-03-17 15:22:29, Andrew Morton wrote:
> On Thu, 30 Mar 2017 13:27:16 +0300 Andrey Ryabinin <aryabinin@virtuozzo.com> wrote:
[...]
> > This can be fixed in vmgfx, but it would be better to make vfree()
> > non-sleeping again because we may have other bugs like this one.
> 
> I tend to disagree: adding yet another schedule_work() introduces
> additional overhead and adds some risk of ENOMEM errors which wouldn't
> occur with a synchronous free.

I do not think ENOMEM would be a problem. We are talking about lazy
handling already. Besides that the allocation path also does this lazy
free AFAICS.

> > __purge_vmap_area_lazy() is the only function in the vfree() path that
> > wants to be able to sleep. So it make sense to schedule
> > __purge_vmap_area_lazy() via schedule_work() so it runs only in sleepable
> > context.
> 
> vfree() already does
> 
> 	if (unlikely(in_interrupt()))
> 		__vfree_deferred(addr);
> 
> so it seems silly to introduce another defer-to-kernel-thread thing
> when we already have one.

But this only cares about the IRQ context and this patch aims at atomic
context in general. I agree it would have been better to reduce this
deferred behavior to only _atomic_ context but we not have a reliable
way to detect that on non-preemptive kernels AFAIR.
-- 
Michal Hocko
SUSE Labs

WARNING: multiple messages have this Message-ID (diff)
From: Michal Hocko <mhocko@kernel.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>,
	penguin-kernel@I-love.SAKURA.ne.jp, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, hpa@zytor.com, chris@chris-wilson.co.uk,
	hch@lst.de, mingo@elte.hu, jszhang@marvell.com,
	joelaf@google.com, joaodias@google.com, willy@infradead.org,
	tglx@linutronix.de, thellstrom@vmware.com,
	stable@vger.kernel.org
Subject: Re: [PATCH 1/4] mm/vmalloc: allow to call vfree() in atomic context
Date: Tue, 4 Apr 2017 11:36:53 +0200	[thread overview]
Message-ID: <20170404093653.GG15132@dhcp22.suse.cz> (raw)
In-Reply-To: <20170330152229.f2108e718114ed77acae7405@linux-foundation.org>

On Thu 30-03-17 15:22:29, Andrew Morton wrote:
> On Thu, 30 Mar 2017 13:27:16 +0300 Andrey Ryabinin <aryabinin@virtuozzo.com> wrote:
[...]
> > This can be fixed in vmgfx, but it would be better to make vfree()
> > non-sleeping again because we may have other bugs like this one.
> 
> I tend to disagree: adding yet another schedule_work() introduces
> additional overhead and adds some risk of ENOMEM errors which wouldn't
> occur with a synchronous free.

I do not think ENOMEM would be a problem. We are talking about lazy
handling already. Besides that the allocation path also does this lazy
free AFAICS.

> > __purge_vmap_area_lazy() is the only function in the vfree() path that
> > wants to be able to sleep. So it make sense to schedule
> > __purge_vmap_area_lazy() via schedule_work() so it runs only in sleepable
> > context.
> 
> vfree() already does
> 
> 	if (unlikely(in_interrupt()))
> 		__vfree_deferred(addr);
> 
> so it seems silly to introduce another defer-to-kernel-thread thing
> when we already have one.

But this only cares about the IRQ context and this patch aims at atomic
context in general. I agree it would have been better to reduce this
deferred behavior to only _atomic_ context but we not have a reliable
way to detect that on non-preemptive kernels AFAIR.
-- 
Michal Hocko
SUSE Labs

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  parent reply	other threads:[~2017-04-04  9:37 UTC|newest]

Thread overview: 65+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-30 10:27 [PATCH 1/4] mm/vmalloc: allow to call vfree() in atomic context Andrey Ryabinin
2017-03-30 10:27 ` Andrey Ryabinin
2017-03-30 10:27 ` Andrey Ryabinin
2017-03-30 10:27 ` [PATCH 2/4] x86/ldt: use vfree() instead of vfree_atomic() Andrey Ryabinin
2017-03-30 10:27   ` Andrey Ryabinin
2017-03-31  8:05   ` Thomas Gleixner
2017-03-31  8:05     ` Thomas Gleixner
2017-03-30 10:27 ` [PATCH 3/4] kernel/fork: use vfree() instead of vfree_atomic() to free thread stack Andrey Ryabinin
2017-03-30 10:27   ` Andrey Ryabinin
2017-03-30 10:27 ` [PATCH 4/4] mm/vmalloc: remove vfree_atomic() Andrey Ryabinin
2017-03-30 10:27   ` Andrey Ryabinin
2017-03-30 17:18   ` Matthew Wilcox
2017-03-30 17:18     ` Matthew Wilcox
2017-03-30 15:27     ` Andrey Ryabinin
2017-03-30 15:27       ` Andrey Ryabinin
2017-04-04  9:40   ` Michal Hocko
2017-04-04  9:40     ` Michal Hocko
2017-03-30 12:00 ` [PATCH 1/4] mm/vmalloc: allow to call vfree() in atomic context Thomas Hellstrom
2017-03-30 12:00   ` Thomas Hellstrom
2017-03-30 12:00   ` Thomas Hellstrom
2017-03-30 14:48   ` Andrey Ryabinin
2017-03-30 14:48     ` Andrey Ryabinin
2017-03-30 14:48     ` Andrey Ryabinin
2017-03-30 15:04     ` Thomas Hellstrom
2017-03-30 15:04       ` Thomas Hellstrom
2017-03-30 15:04       ` Thomas Hellstrom
2017-04-04  9:41     ` Michal Hocko
2017-04-04  9:41       ` Michal Hocko
2017-04-04  9:49       ` Thomas Hellstrom
2017-04-04  9:49         ` Thomas Hellstrom
2017-04-04  9:49         ` Thomas Hellstrom
2017-04-05 10:31       ` Andrey Ryabinin
2017-04-05 10:31         ` Andrey Ryabinin
2017-04-05 10:31         ` Andrey Ryabinin
2017-04-05 10:42         ` Michal Hocko
2017-04-05 10:42           ` Michal Hocko
2017-04-05 11:42     ` Vlastimil Babka
2017-04-05 11:42       ` Vlastimil Babka
2017-04-05 12:14       ` Michal Hocko
2017-04-05 12:14         ` Michal Hocko
2017-03-30 22:22 ` Andrew Morton
2017-03-30 22:22   ` Andrew Morton
2017-03-30 22:22   ` Andrew Morton
2017-03-31  7:12   ` Joel Fernandes
2017-03-31  7:12     ` Joel Fernandes
2017-03-31  9:26   ` Andrey Ryabinin
2017-03-31  9:26     ` Andrey Ryabinin
2017-03-31  9:26     ` Andrey Ryabinin
2017-04-04  9:36   ` Michal Hocko [this message]
2017-04-04  9:36     ` Michal Hocko
2017-04-04  9:38 ` Michal Hocko
2017-04-04  9:38   ` Michal Hocko
2017-04-12 12:49 ` [PATCH v2 0/5] " Andrey Ryabinin
2017-04-12 12:49   ` Andrey Ryabinin
2017-04-12 12:49   ` [PATCH v2 1/5] mm/vmalloc: " Andrey Ryabinin
2017-04-12 12:49     ` Andrey Ryabinin
2017-04-12 12:49     ` Andrey Ryabinin
2017-04-12 12:49   ` [PATCH v2 2/5] x86/ldt: use vfree() instead of vfree_atomic() Andrey Ryabinin
2017-04-12 12:49     ` Andrey Ryabinin
2017-04-12 12:49   ` [PATCH v2 3/5] kernel/fork: use vfree() instead of vfree_atomic() to free thread stack Andrey Ryabinin
2017-04-12 12:49     ` Andrey Ryabinin
2017-04-12 12:49   ` [PATCH v2 4/5] mm/vmalloc: remove vfree_atomic() Andrey Ryabinin
2017-04-12 12:49     ` Andrey Ryabinin
2017-04-12 12:49   ` [PATCH v2 5/5] mm/vmalloc: Don't spawn workers if somebody already purging Andrey Ryabinin
2017-04-12 12:49     ` Andrey Ryabinin

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