linux-kernel - Re: [PATCH 3/3] percpu: allow select gfp to be passed to underlying allocators

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Date:   Thu, 15 Feb 2018 17:17:14 -0600
From:   Dennis Zhou <dennisszhou@...il.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Christoph Lameter <cl@...ux.com>,
        Daniel Borkmann <daniel@...earbox.net>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] percpu: allow select gfp to be passed to underlying
 allocators

Hi,

On Thu, Feb 15, 2018 at 01:41:48PM -0800, Tejun Heo wrote:
> On Thu, Feb 15, 2018 at 10:08:16AM -0600, Dennis Zhou wrote:
> > +/* the whitelisted flags that can be passed to the backing allocators */
> > +#define gfp_percpu_mask(gfp) (((gfp) & (__GFP_NORETRY | __GFP_NOWARN)) | \
> > +			      GFP_KERNEL)
> 
> Isn't there just one place where gfp comes in from outside?  If so,
> this looks like a bit of overkill.  Can't we just filter there?
> 

I agree, but it's also nice having a single place where flags can be
added or removed. The primary motivator was for the "| GFP_KERNEL", but
as suggested in the other patch this is getting removed. I guess I still
lean towards having it as it's explicit and helps gate both the balance
path and the user allocation path.

Thanks,
Dennis