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From: Joel Fernandes <joelaf@google.com>
Date: Fri, 4 Nov 2016 20:43:16 -0700
Message-ID: <CAJWu+oppRL5kD9qPcdCbFAbEkE7bN+kmrvTuaueVZnY+WtK_tg@mail.gmail.com>
Subject: Re: [PATCH 4/7] mm: defer vmalloc from atomic context
To: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Christoph Hellwig <hch@lst.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jisheng Zhang <jszhang@marvell.com>,
        Chris Wilson <chris@chris-wilson.co.uk>,
        John Dias <joaodias@google.com>,
        "open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>,
        linux-rt-users@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>
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On Mon, Oct 24, 2016 at 8:44 AM, Andrey Ryabinin
<aryabinin@virtuozzo.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@lst.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?

Thanks,
Joel