linux-kernel - Re: [RFC PATCH 1/1] mm/percpu.c: fix several trivial issues

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Message-ID: <fdaf7005-13f0-00f1-7143-fd5cac586641@zoho.com>
Date:   Fri, 14 Oct 2016 08:56:37 +0800
From:   zijun_hu <zijun_hu@...o.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     zijun_hu@....com, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org, cl@...ux.com
Subject: Re: [RFC PATCH 1/1] mm/percpu.c: fix several trivial issues

On 2016/10/14 8:34, Tejun Heo wrote:
> On Tue, Oct 11, 2016 at 09:29:27PM +0800, zijun_hu wrote:
>> From: zijun_hu <zijun_hu@....com>
>>
>> as shown by pcpu_setup_first_chunk(), the first chunk is same as the
>> reserved chunk if the reserved size is nonzero but the dynamic is zero
>> this special scenario is referred as the special case by below content
>>
>> fix several trivial issues:
>>
>> 1) correct or fix several comments
>> the LSB of a chunk->map element is used as free/in-use flag and is cleared
>> for free area and set for in-use, rather than use positive/negative number
>> to mark area state.
>>
>> 2) change atomic size to PAGE_SIZE for consistency when CONFIG_SMP == n
>> both default setup_per_cpu_areas() and pcpu_page_first_chunk()
>> use PAGE_SIZE as atomic size when CONFIG_SMP == y; however
>> setup_per_cpu_areas() allocates memory for the only unit with alignment
>> PAGE_SIZE but assigns unit size to atomic size when CONFIG_SMP == n, so the
>> atomic size isn't consistent with either the alignment or the SMP ones.
>> fix it by changing atomic size to PAGE_SIZE when CONFIG_SMP == n
>>
>> 3) correct empty and populated pages statistic error
>> in order to service dynamic atomic memory allocation, the number of empty
>> and populated pages of chunks is counted to maintain above a low threshold.
>> however, for the special case, the first chunk is took into account by
>> pcpu_setup_first_chunk(), it is meaningless since the chunk don't include
>> any dynamic areas.
>> fix it by excluding the reserved chunk before statistic as the other
>> contexts do.
>>
>> 4) fix potential memory leakage for percpu_init_late()
>> in order to manage chunk->map memory uniformly, for the first and reserved
>> chunks, percpu_init_late() will allocate memory to replace the static
>> chunk->map array within section .init.data after slab is brought up
>> however, for the special case, memory are allocated for the same chunk->map
>> twice since the first chunk reference is same as the reserved, so the
>> memory allocated at the first time are leaked obviously.
>> fix it by eliminating the second memory allocation under the special case
>>
>> Signed-off-by: zijun_hu <zijun_hu@....com>
> 
> Can you please break the changes into separate patches?
  yes, i can
  could you give many comments for that trivial issues firstly?
  i will separate and product which you thinks reasonable formally.
  thanks
> 
> Thanks.
>