linux-kernel - Re: [PATCH] mm: clear __GFP_FS when PF_MEMALLOC

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Date:	Thu, 04 Sep 2014 10:18:18 +0800
From:	Junxiao Bi <junxiao.bi@...cle.com>
To:	Trond Myklebust <trond.myklebust@...marydata.com>
CC:	david@...morbit.com, akpm@...ux-foundation.org,
	xuejiufei@...wei.com, ming.lei@...onical.com,
	Linux Kernel mailing list <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, Devel FS Linux <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] mm: clear __GFP_FS when PF_MEMALLOC_NOIO is set

On 09/03/2014 08:20 PM, Trond Myklebust wrote:
> On Wed, Sep 3, 2014 at 1:54 AM, Junxiao Bi <junxiao.bi@...cle.com> wrote:
>> commit 21caf2fc1931 ("mm: teach mm by current context info to not do I/O during memory allocation")
>> introduces PF_MEMALLOC_NOIO flag to avoid doing I/O inside memory allocation, __GFP_IO is cleared
>> when this flag is set, but __GFP_FS implies __GFP_IO, it should also be cleared. Or it may still
>> run into I/O, like in superblock shrinker.
>>
>> Signed-off-by: Junxiao Bi <junxiao.bi@...cle.com>
>> Cc: joyce.xue <xuejiufei@...wei.com>
>> Cc: Ming Lei <ming.lei@...onical.com>
>> ---
>>  include/linux/sched.h |    6 ++++--
>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>> index 5c2c885..2fb2c47 100644
>> --- a/include/linux/sched.h
>> +++ b/include/linux/sched.h
>> @@ -1936,11 +1936,13 @@ extern void thread_group_cputime_adjusted(struct task_struct *p, cputime_t *ut,
>>  #define tsk_used_math(p) ((p)->flags & PF_USED_MATH)
>>  #define used_math() tsk_used_math(current)
>>
>> -/* __GFP_IO isn't allowed if PF_MEMALLOC_NOIO is set in current->flags */
>> +/* __GFP_IO isn't allowed if PF_MEMALLOC_NOIO is set in current->flags
>> + * __GFP_FS is also cleared as it implies __GFP_IO.
>> + */
>>  static inline gfp_t memalloc_noio_flags(gfp_t flags)
>>  {
>>         if (unlikely(current->flags & PF_MEMALLOC_NOIO))
>> -               flags &= ~__GFP_IO;
>> +               flags &= ~(__GFP_IO | __GFP_FS);
>>         return flags;
>>  }
>>
> 
> Shouldn't this be a stable fix? If it is needed, then it will affect
> all kernels that define PF_MEMALLOC_NOIO.
Yes, should be. An ocfs2 deadlock bug related to this.

Thanks,
Junxiao.
> 

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