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

[Scott Wood]

On Tue, 2015-09-01 at 22:57 -0500, Zhao Qiang-B45475 wrote:
> On Wed, 2015-09-02 at 10:33AM -0500, Wood Scott-B07421 wrote:
> > -----Original Message-----
> > From: Wood Scott-B07421
> > Sent: Wednesday, September 02, 2015 11:09 AM
> > To: Zhao Qiang-B45475
> > Cc: linux-kernel@xxxxxxxxxxxxxxx; linuxppc-dev@xxxxxxxxxxxxxxxx;
> > lauraa@xxxxxxxxxxxxxx; Xie Xiaobo-R63061; benh@xxxxxxxxxxxxxxxxxxx; Li
> > Yang-Leo-R58472; paulus@xxxxxxxxx
> > Subject: Re: [PATCH V7 1/3] genalloc:support memory-allocation with
> > bytes-alignment to genalloc
> > 
> > On Tue, 2015-09-01 at 22:05 -0500, Zhao Qiang-B45475 wrote:
> > > On Wed, 2015-09-02 at 10:33AM -0500, Wood Scott-B07421 wrote:
> > > 
> > > > -----Original Message-----
> > > > From: Wood Scott-B07421
> > > > Sent: Wednesday, September 02, 2015 10:33 AM
> > > > To: Zhao Qiang-B45475
> > > > Cc: linux-kernel@xxxxxxxxxxxxxxx; linuxppc-dev@xxxxxxxxxxxxxxxx;
> > > > lauraa@xxxxxxxxxxxxxx; Xie Xiaobo-R63061; benh@xxxxxxxxxxxxxxxxxxx;
> > > > Li Yang-Leo-R58472; paulus@xxxxxxxxx
> > > > 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@xxxxxxxxxxxxxxx; linuxppc-dev@xxxxxxxxxxxxxxxx;
> > > > > > lauraa@xxxxxxxxxxxxxx; Xie Xiaobo-R63061;
> > > > > > benh@xxxxxxxxxxxxxxxxxxx; Li Yang-Leo-R58472; paulus@xxxxxxxxx
> > > > > > 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@xxxxxxxxxxxxxxx;
> > > > > > > > linuxppc-dev@xxxxxxxxxxxxxxxx; lauraa@xxxxxxxxxxxxxx; Xie
> > > > > > > > Xiaobo-R63061; benh@xxxxxxxxxxxxxxxxxxx; Li Yang-Leo-R58472;
> > > > > > > > paulus@xxxxxxxxx
> > > > > > > > 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@xxxxxxxxxxxxx>
> > > > > > > > > ---
> > > > > > > > > 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?
> > > 
> > > Yes, 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.
> > > 
> > > Add a function? Do you mean add a new alloc function or new algo?
> > > If you mean new algo, CPM use both align algo and new algo, set
> > > Different algos in different muram_alloc func?
> > 
> > I was thinking that it was a sufficiently different operation that it
> > warranted its own independent function, but I suppose you could do it as
> > an algorithm that only accepts the requested range and returns failure
> > for all other chunks (as well as if the range is unavailable).  It would
> > not be related at all to the aligned-alloc algorithm.
> 
> If do so, I need set algo in different muram_alloc function, it is 
> redundancy.

If you do it as a separate top-level function there would be no algorithm.

Using an algorithm would be simpler to implement, but a bit more awkward in 
the caller due to the need to swap out the algorithm (unless we change 
gen_pool_alloc_data to gen_pool_alloc_algo_data or similar...).

> The algos has start para, but it set start_bit = 0 in gen_pool_alloc_data, 
> can We pass a start addr para to gen_pool_alloc_data?

No.  Again, setting that "start" variable is not equivalent to what you're 
trying to accomplish, even if it happens to work in your test case.

-Scott

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