linux-kernel - Re: [PATCH v4] mm: cma: support sysfs

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Date:   Fri, 19 Mar 2021 12:03:46 -0700
From:   Minchan Kim <minchan@...nel.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>, joaodias@...gle.com,
        willy@...radead.org, david@...hat.com, surenb@...gle.com,
        John Hubbard <jhubbard@...dia.com>,
        Nicolas Chauvet <kwizart@...il.com>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v4] mm: cma: support sysfs

On Fri, Mar 19, 2021 at 09:48:11PM +0300, Dmitry Osipenko wrote:
> 19.03.2021 21:21, Minchan Kim пишет:
> > On Fri, Mar 19, 2021 at 08:56:06PM +0300, Dmitry Osipenko wrote:
> >> 19.03.2021 19:30, Minchan Kim пишет:
> >>> +static void cma_kobj_release(struct kobject *kobj)
> >>> +{
> >>> +	struct cma_kobject *cma_kobj = container_of(kobj, struct cma_kobject, kobj);
> >>> +
> >>> +	kfree(cma_kobj);
> >>> +}
> >>
> >> Oh, wait.. I think this kfree wrong since cma_kobj belongs to the array.
> > 
> > Oh, good spot. Let me use kzalloc.
> > 
> 
> Thinking a bit more about this.. it looks like actually it should be
> better to get back to the older variant of cma_stat, but allocate at the
> time of CMA initialization, rather than at the time of sysfs
> initialization. Then the cma_stat will be decoupled from the cma struct

IIRC, the problem was slab was not initiaized at CMA init point.
That's why I liked your suggestion.

> and cma_stat will be a self-contained object.

Yeah, self-contained is better but it's already weird to
have differnt lifetime for one object since CMA object
never die, technically.