linux-kernel - Re: [PATCH V7 1/3] genalloc:support memory-allocation with bytes-alignment to genalloc

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Message-ID: <1441161203.4966.126.camel@freescale.com>
Date:	Tue, 1 Sep 2015 21:33:23 -0500
From:	Scott Wood <scottwood@...escale.com>
To:	Zhao Qiang-B45475 <qiang.zhao@...escale.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"lauraa@...eaurora.org" <lauraa@...eaurora.org>,
	Xie Xiaobo-R63061 <X.Xie@...escale.com>,
	"benh@...nel.crashing.org" <benh@...nel.crashing.org>,
	Li Yang-Leo-R58472 <LeoLi@...escale.com>,
	"paulus@...ba.org" <paulus@...ba.org>
Subject: Re: [PATCH V7 1/3] genalloc:support memory-allocation with
 bytes-alignment to genalloc

On Tue, 2015-09-01 at 21:29 -0500, Zhao Qiang-B45475 wrote:
> On Wed, 2015-09-02 at 10:18AM -0500, Wood Scott-B07421 wrote:
> > -----Original Message-----
> > From: Wood Scott-B07421
> > Sent: Wednesday, September 02, 2015 10:18 AM
> > To: Zhao Qiang-B45475
> > Cc: linux-kernel@...r.kernel.org; linuxppc-dev@...ts.ozlabs.org;
> > lauraa@...eaurora.org; Xie Xiaobo-R63061; benh@...nel.crashing.org; Li
> > Yang-Leo-R58472; paulus@...ba.org
> > Subject: Re: [PATCH V7 1/3] genalloc:support memory-allocation with
> > bytes-alignment to genalloc
> > 
> > On Tue, 2015-09-01 at 21:10 -0500, Zhao Qiang-B45475 wrote:
> > > On Wed, 2015-09-02 at 08:38AM +0800, Wood Scott-B07421 wrote:
> > > > -----Original Message-----
> > > > From: Wood Scott-B07421
> > > > Sent: Wednesday, September 02, 2015 8:30 AM
> > > > To: Zhao Qiang-B45475
> > > > Cc: linux-kernel@...r.kernel.org; linuxppc-dev@...ts.ozlabs.org;
> > > > lauraa@...eaurora.org; Xie Xiaobo-R63061; benh@...nel.crashing.org;
> > > > Li Yang-Leo-R58472; paulus@...ba.org
> > > > Subject: Re: [PATCH V7 1/3] genalloc:support memory-allocation with
> > > > bytes-alignment to genalloc
> > > > 
> > > > On Mon, 2015-08-31 at 16:58 +0800, Zhao Qiang wrote:
> > > > > Bytes alignment is required to manage some special RAM, so add
> > > > > gen_pool_first_fit_align to genalloc, meanwhile add
> > > > > gen_pool_alloc_data to pass data to
> > > > > gen_pool_first_fit_align(modify gen_pool_alloc as a wrapper)
> > > > > 
> > > > > Signed-off-by: Zhao Qiang <qiang.zhao@...escale.com>
> > > > > ---
> > > > > Changes for v6:
> > > > >       - patches set v6 include a new patch because of using
> > > > >       - genalloc to manage QE MURAM, patch 0001 is the new
> > > > >       - patch, adding bytes alignment for allocation for use.
> > > > > Changes for v7:
> > > > >       - cpm muram also need to use genalloc to manage, it has
> > > > >         a function to reserve a specific region of muram,
> > > > >         add offset to genpool_data for start addr to be allocated.
> > > > 
> > > > This seems to be describing more than just the changes in this patch.
> > > > What does also handling cpm have to do with this patch?  Are you
> > > > adding support for reserving a specific region in this patch?  I
> > > > don't see it, and in any case it should go in a different patch.
> > > 
> > > Yes, I added. The code below can support the function.
> > >       offset_bit = (alignment->offset + (1UL << order) - 1) >> order;
> > >       return bitmap_find_next_zero_area(map, size, start + offset_bit,
> > nr,
> > >                         align_mask);
> > > 
> > > CPM has an function cpm_muram_alloc_fixed, needing to allocate muram
> > > from a Specific offset. So I add the code and add offset to struct data.
> > 
> > I thought the offset was related to the previous discussion of checking
> > for allocation failure.  Are you using it to implement alloc_fixed()?  If
> > so, please don't.  Besides the awkward implementation (what does it
> > logically have to do with gen_pool_first_fit_align?), it does not appear
> > to be correct -
> > - what happens with multiple chunks?  What happens if part of the region
> > the caller is trying to reserve is already taken?  Implement a proper
> > function to reserve a fixed genalloc region.
> 
> This offset is totally different with the workaround OFFSET!

There's a reason why we write changelogs that describe what the patch is 
doing, and avoid combining logically distinct changes in the same patch.

> This offset is the offset of the muram.

The offset of the muram relative to what?  Or do you mean the offset into 
muram?

> CPM need to allocate block from a specific offset due to hardware 
> restriction.
> So I must handle this offset in genalloc. 

Again, if you need to be able to mark a specific range reserved, add a 
function that does that properly.  Don't try to hack it in the way you did.

-Scott

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