diff mbox series

[1/2] perpcu: correct pcpu_find_block_fit comments

Message ID 20190304104541.25745-1-peng.fan@nxp.com (mailing list archive)
State New, archived
Headers show
Series [1/2] perpcu: correct pcpu_find_block_fit comments | expand

Commit Message

Peng Fan March 4, 2019, 10:33 a.m. UTC 
pcpu_find_block_fit is not find block index, it is to find
the bitmap off in a chunk.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
---

V1:
  Based on https://patchwork.kernel.org/cover/10832459/ applied linux-next

 mm/percpu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Dennis Zhou March 4, 2019, 7:13 p.m. UTC | #1 
On Mon, Mar 04, 2019 at 10:33:52AM +0000, Peng Fan wrote:
> pcpu_find_block_fit is not find block index, it is to find
> the bitmap off in a chunk.
> 
> Signed-off-by: Peng Fan <peng.fan@nxp.com>
> ---
> 
> V1:
>   Based on https://patchwork.kernel.org/cover/10832459/ applied linux-next
> 
>  mm/percpu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/percpu.c b/mm/percpu.c
> index 7f630d5469e8..5ee90fc34ea3 100644
> --- a/mm/percpu.c
> +++ b/mm/percpu.c
> @@ -1061,7 +1061,7 @@ static bool pcpu_is_populated(struct pcpu_chunk *chunk, int bit_off, int bits,
>  }
>  
>  /**
> - * pcpu_find_block_fit - finds the block index to start searching
> + * pcpu_find_block_fit - finds the offset in chunk bitmap to start searching
>   * @chunk: chunk of interest
>   * @alloc_bits: size of request in allocation units
>   * @align: alignment of area (max PAGE_SIZE bytes)
> -- 
> 2.16.4
> 

So really the block index is encoded in the bit offset. I'm not super
happy with either wording because the point of the function really is to
find a block(s) that can support this allocation and it happens the
output is a chunk offset.

Thanks,
Dennis
Peng Fan March 5, 2019, 1:49 a.m. UTC | #2 
> -----Original Message-----
> From: Dennis Zhou [mailto:dennis@kernel.org]
> Sent: 2019年3月5日 3:14
> To: Peng Fan <peng.fan@nxp.com>
> Cc: tj@kernel.org; cl@linux.com; linux-mm@kvack.org;
> linux-kernel@vger.kernel.org; van.freenix@gmail.com
> Subject: Re: [PATCH 1/2] perpcu: correct pcpu_find_block_fit comments
> 
> On Mon, Mar 04, 2019 at 10:33:52AM +0000, Peng Fan wrote:
> > pcpu_find_block_fit is not find block index, it is to find the bitmap
> > off in a chunk.
> >
> > Signed-off-by: Peng Fan <peng.fan@nxp.com>
> > ---
> >
> > V1:
> >   Based on
> >
> https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpat
> >
> chwork.kernel.org%2Fcover%2F10832459%2F&amp;data=02%7C01%7Cpeng.
> fan%40
> >
> nxp.com%7Cebb4d3d31dca4c76ec2e08d6a0d587fd%7C686ea1d3bc2b4c6fa9
> 2cd99c5
> >
> c301635%7C0%7C0%7C636873236308905172&amp;sdata=POM0aLB5P7g3y
> p6oD5s8uDY
> > 629jfIeo4hko4PcqNA70%3D&amp;reserved=0 applied linux-next
> >
> >  mm/percpu.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/mm/percpu.c b/mm/percpu.c index
> > 7f630d5469e8..5ee90fc34ea3 100644
> > --- a/mm/percpu.c
> > +++ b/mm/percpu.c
> > @@ -1061,7 +1061,7 @@ static bool pcpu_is_populated(struct pcpu_chunk
> > *chunk, int bit_off, int bits,  }
> >
> >  /**
> > - * pcpu_find_block_fit - finds the block index to start searching
> > + * pcpu_find_block_fit - finds the offset in chunk bitmap to start
> > + searching
> >   * @chunk: chunk of interest
> >   * @alloc_bits: size of request in allocation units
> >   * @align: alignment of area (max PAGE_SIZE bytes)
> > --
> > 2.16.4
> >
> 
> So really the block index is encoded in the bit offset. I'm not super
> happy with either wording because the point of the function really is to
> find a block(s) that can support this allocation and it happens the
> output is a chunk offset.

I just think the comments is confusing, because block_index is not used in
this function or returned. However the function returns a bit offset
in a chunk for caller's. I understand block index is encoded in the bit offset as following
            block_index     
              |
              v
Block   |----|----|----|----|----|----|----|----|----|----|
Chunk  |------------------------------------------------------|
                |
                V
               bit_off in a chunk
and bit_off = block_index * PCPU_BITMAP_BLOCK_BITS + offset in a block

I'll leave it as is, since you not prefer.

Thanks,
Peng.
> 
> Thanks,
> Dennis
diff mbox series

Patch

diff --git a/mm/percpu.c b/mm/percpu.c
index 7f630d5469e8..5ee90fc34ea3 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1061,7 +1061,7 @@  static bool pcpu_is_populated(struct pcpu_chunk *chunk, int bit_off, int bits,
 }
 
 /**
- * pcpu_find_block_fit - finds the block index to start searching
+ * pcpu_find_block_fit - finds the offset in chunk bitmap to start searching
  * @chunk: chunk of interest
  * @alloc_bits: size of request in allocation units
  * @align: alignment of area (max PAGE_SIZE bytes)