linux-kernel - Re: [PATCH v5] mm: cma: support sysfs

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Message-ID: <YFrR6TQckcuDdgeT@google.com>
Date:   Tue, 23 Mar 2021 22:45:13 -0700
From:   Minchan Kim <minchan@...nel.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>, gregkh@...uxfoundation.org,
        surenb@...gle.com, joaodias@...gle.com, jhubbard@...dia.com,
        digetx@...il.com
Subject: Re: [PATCH v5] mm: cma: support sysfs

On Wed, Mar 24, 2021 at 04:34:34AM +0000, Matthew Wilcox wrote:
> On Tue, Mar 23, 2021 at 08:31:31PM -0700, Minchan Kim wrote:
> > On Wed, Mar 24, 2021 at 03:02:24AM +0000, Matthew Wilcox wrote:
> > > On Tue, Mar 23, 2021 at 12:50:50PM -0700, Minchan Kim wrote:
> > > > +	/* the number of CMA page successful allocations */
> > > > +	atomic64_t nr_pages_succeeded;
> > > 
> > > > +void cma_sysfs_alloc_pages_count(struct cma *cma, size_t count)
> > > > +{
> > > > +	atomic64_add(count, &cma->nr_pages_succeeded);
> > > > +}
> > > 
> > > I don't understand.  A size_t is a byte count.  But the variable is called
> > > 'nr_pages'.  So which is it, a byte count or a page count?
> > 
> > It's page count. I followed the cma_alloc interface since it has
> > size_t count variable for nr_pages.
> 
> That's very confusing.  cma_alloc is wrong; if it needs to be an
> unsigned long, that's fine.  But it shouldn't be size_t.
> 
> 7.17 of n1256 defines:
> 
> 	size_t
> which is the unsigned integer type of the result of the sizeof operator
> 
> Do you want to submit a patch to fix cma_alloc as well?

Sure, but it will be separate patch.

> 
> > Let's go with unsigned long nr_pages:
> > void cma_sysfs_alloc_pages_count(struct cma *cma, unsigned long
> > nr_pages)
> 
> Works for me!

Thanks for review!