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

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Date:   Thu, 13 Oct 2016 20:34:26 -0400
From:   Tejun Heo <tj@...nel.org>
To:     zijun_hu <zijun_hu@...o.com>
Cc:     akpm@...ux-foundation.org, zijun_hu@....com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, cl@...ux.com
Subject: Re: [RFC PATCH 1/1] mm/percpu.c: fix several trivial issues

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?

Thanks.

-- 
tejun