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Date: Mon, 7 Nov 2016 08:50:46 -0800 From: Joel Fernandes <joelaf@...gle.com> To: Andrey Ryabinin <aryabinin@...tuozzo.com> Cc: 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 7, 2016 at 7:01 AM, Andrey Ryabinin <aryabinin@...tuozzo.com> wrote: > On 11/05/2016 06:43 AM, Joel Fernandes wrote: >> On Mon, Oct 24, 2016 at 8:44 AM, Andrey Ryabinin >> <aryabinin@...tuozzo.com> wrote: >>> >>> >>> On 10/22/2016 06:17 PM, Christoph Hellwig wrote: >>>> We want to be able to use a sleeping lock for freeing vmap to keep >>>> latency down. For this we need to use the deferred vfree mechanisms >>>> no only from interrupt, but from any atomic context. >>>> >>>> Signed-off-by: Christoph Hellwig <hch@....de> >>>> --- >>>> mm/vmalloc.c | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/mm/vmalloc.c b/mm/vmalloc.c >>>> index a4e2cec..bcc1a64 100644 >>>> --- a/mm/vmalloc.c >>>> +++ b/mm/vmalloc.c >>>> @@ -1509,7 +1509,7 @@ void vfree(const void *addr) >>>> >>>> if (!addr) >>>> return; >>>> - if (unlikely(in_interrupt())) { >>>> + if (unlikely(in_atomic())) { >>> >>> in_atomic() cannot always detect atomic context, thus it shouldn't be used here. >>> You can add something like vfree_in_atomic() and use it in atomic call sites. >>> >> >> 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. Yes, this sounds like a better idea as there may not be that many callers and my idea may hurt perf. Thanks, Joel
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