linux-kernel - Re: Re: Re: [PATCH v6 02/14] mm/damon: Implement region based sampling

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Message-ID: <20200317113205.3617-1-sjpark@amazon.com>
Date:   Tue, 17 Mar 2020 12:32:05 +0100
From:   SeongJae Park <sjpark@...zon.com>
To:     SeongJae Park <sj38.park@...il.com>
CC:     Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        SeongJae Park <sjpark@...zon.com>, <akpm@...ux-foundation.org>,
        SeongJae Park <sjpark@...zon.de>, <aarcange@...hat.com>,
        <yang.shi@...ux.alibaba.com>, <acme@...nel.org>,
        <alexander.shishkin@...ux.intel.com>, <amit@...nel.org>,
        <brendan.d.gregg@...il.com>, <brendanhiggins@...gle.com>,
        <cai@....pw>, <colin.king@...onical.com>, <corbet@....net>,
        <dwmw@...zon.com>, <jolsa@...hat.com>, <kirill@...temov.name>,
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        <rostedt@...dmis.org>, <shuah@...nel.org>, <vbabka@...e.cz>,
        <vdavydov.dev@...il.com>, <linux-mm@...ck.org>,
        <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: Re: Re: [PATCH v6 02/14] mm/damon: Implement region based sampling

On Fri, 13 Mar 2020 21:16:49 +0100 SeongJae Park <sj38.park@...il.com> wrote:

> On Fri, 13 Mar 2020 17:29:54 +0000 Jonathan Cameron <Jonathan.Cameron@...wei.com> wrote:
> 
> > On Mon, 24 Feb 2020 13:30:35 +0100
> > SeongJae Park <sjpark@...zon.com> wrote:
> > 
> > > From: SeongJae Park <sjpark@...zon.de>
> > > 
> > > This commit implements DAMON's basic access check and region based
> > > sampling mechanisms.  This change would seems make no sense, mainly
> > > because it is only a part of the DAMON's logics.  Following two commits
> > > will make more sense.
> > > 
> [...]
> > 
> > Came across a minor issue inline.  kthread_run calls kthread_create.
> > That gives a potential sleep while atomic issue given the spin lock.
> > 
> > Can probably be fixed by preallocating the thread then starting it later.
> > 
> > Jonathan
> [...]
> > > +/*
> > > + * Start or stop the kdamond
> > > + *
> > > + * Returns 0 if success, negative error code otherwise.
> > > + */
> > > +static int damon_turn_kdamond(struct damon_ctx *ctx, bool on)
> > > +{
> > > +	spin_lock(&ctx->kdamond_lock);
> > > +	ctx->kdamond_stop = !on;
> > > +	if (!ctx->kdamond && on) {
> > > +		ctx->kdamond = kthread_run(kdamond_fn, ctx, "kdamond");
> > 
> > Can't do this under a spin lock.
> 
> Good catch!  And, agree to your suggestion.  I will fix this in that way!

I changed my mind.  I would like to simply use mutex instead of spinlock, as
khugepaged also does.  If you have different opinion, please let me know.


Thanks,
SeongJae Park

> 
> 
> Thanks,
> SeongJae Park