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

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Date:	Thu, 10 Sep 2015 21:15:00 -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 Thu, 2015-09-10 at 21:09 -0500, Zhao Qiang-B45475 wrote:
> On Fri, 2015-09-11 at 06:07AM -0500, Wood Scott-B07421 wrote:
> > -----Original Message-----
> > From: Wood Scott-B07421
> > Sent: Friday, September 11, 2015 6:07 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 Wed, 2015-09-09 at 21:26 -0500, Zhao Qiang-B45475 wrote:
> > > On Wed, 2015-09-10 at 12:38AM -0500, Wood Scott-B07421 wrote:
> > > > -----Original Message-----
> > > > From: Wood Scott-B07421
> > > > Sent: Thursday, September 10, 2015 12:38 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 Sat, 2015-09-05 at 22:13 -0500, Zhao Qiang-B45475 wrote:
> > > > > On Wed, 2015-09-02 at 10:18AM +0800, 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.
> > > > > > 
> > > > > The offset is which allocation block address need to be larger
> > > > > than, Not equal to, it really like the parameter start of the
> > > > > algo(the bitnumber To start searching at).
> > > > 
> > > > cpm_muram_alloc_fixed() is not "search starting at this offset".  It
> > > > is "reserve this exact range or fail".
> > > 
> > > Yes, you are right! How about to add a new algo into genalloc to
> > > search At offset, then handle it in muram layer, if the address return
> > > from genalloc Is not equal to offset, return negative number?
> > 
> > If you're adding a new algorithm, why not make it actually do what you
> > want rather than adding something different and fixing it up in the
> > caller?
> 
> Because I'm not sure whether it is proper to add a "offset searching at" 
> algo. 

Again, "offset searching at" is not what we want anyway.  What we want is 
"allocate this range or fail".  Why would it be improper to have such an 
algorithm?

-Scott

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