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Subject: Re: [RFC PATCH] memalloc_noio: update the comment to make it cleaner
To:     Michal Hocko <mhocko@kernel.org>
Cc:     mingo@redhat.com, peterz@infradead.org, akpm@linux-foundation.org,
        linux-kernel@vger.kernel.org
References: <20190917232820.23504-1-xiubli@redhat.com>
 <20190918072542.GC12770@dhcp22.suse.cz>
From:   Xiubo Li <xiubli@redhat.com>
Message-ID: <315246db-ec28-f5e0-e9b3-eba0cb60b796@redhat.com>
Date:   Wed, 18 Sep 2019 16:02:52 +0800
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On 2019/9/18 15:25, Michal Hocko wrote:
> On Wed 18-09-19 04:58:20, xiubli@redhat.com wrote:
>> From: Xiubo Li <xiubli@redhat.com>
>>
>> The GFP_NOIO means all further allocations will implicitly drop
>> both __GFP_IO and __GFP_FS flags and so they are safe for both the
>> IO critical section and the the critical section from the allocation
>> recursion point of view. Not only the __GFP_IO, which a bit confusing
>> when reading the code or using the save/restore pair.
> Historically GFP_NOIO has always implied GFP_NOFS as well. I can imagine
> that this might come as an surprise for somebody not familiar with the
> code though.

Yeah, it true.

>   I am wondering whether your update of the documentation
> would be better off at __GFP_FS, __GFP_IO resp. GFP_NOFS, GFP_NOIO level.
> This interface is simply a way to set a scoped NO{IO,FS} context.

The "Documentation/core-api/gfp_mask-from-fs-io.rst" is already very 
detail about them all.

This fixing just means to make sure that it won't surprise someone who 
is having a quickly through some code and not familiar much about the 
detail. It may make not much sense ?

Thanks,
BRs
Xiubo


>> Signed-off-by: Xiubo Li <xiubli@redhat.com>
>> ---
>>   include/linux/sched/mm.h | 9 +++++----
>>   1 file changed, 5 insertions(+), 4 deletions(-)
>>
>> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
>> index 4a7944078cc3..9bdc97e52de1 100644
>> --- a/include/linux/sched/mm.h
>> +++ b/include/linux/sched/mm.h
>> @@ -211,10 +211,11 @@ static inline void fs_reclaim_release(gfp_t gfp_mask) { }
>>    * memalloc_noio_save - Marks implicit GFP_NOIO allocation scope.
>>    *
>>    * This functions marks the beginning of the GFP_NOIO allocation scope.
>> - * All further allocations will implicitly drop __GFP_IO flag and so
>> - * they are safe for the IO critical section from the allocation recursion
>> - * point of view. Use memalloc_noio_restore to end the scope with flags
>> - * returned by this function.
>> + * All further allocations will implicitly drop __GFP_IO and __GFP_FS
>> + * flags and so they are safe for both the IO critical section and the
>> + * the critical section from the allocation recursion point of view. Use
>> + * memalloc_noio_restore to end the scope with flags returned by this
>> + * function.
>>    *
>>    * This function is safe to be used from any context.
>>    */
>> -- 
>> 2.21.0