linux-kernel - Re: [PATCH 1/2] test_xarray: add tests for advanced multi-index use

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Date: Fri, 26 Jan 2024 19:26:17 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Luis Chamberlain <mcgrof@...nel.org>
Cc: kernel test robot <oliver.sang@...el.com>,
	Daniel Gomez <da.gomez@...sung.com>, oe-lkp@...ts.linux.dev,
	lkp@...el.com, linux-kernel@...r.kernel.org,
	"gost.dev@...sung.com" <gost.dev@...sung.com>,
	Pankaj Raghav <p.raghav@...sung.com>
Subject: Re: [PATCH 1/2] test_xarray: add tests for advanced multi-index use

On Fri, Jan 26, 2024 at 11:12:03AM -0800, Luis Chamberlain wrote:
> On Fri, Nov 17, 2023 at 01:01:18PM -0800, Luis Chamberlain wrote:
> > On Fri, Nov 17, 2023 at 08:58:05PM +0000, Matthew Wilcox wrote:
> > > On Fri, Nov 17, 2023 at 12:54:09PM -0800, Luis Chamberlain wrote:
> > > > +/*
> > > > + * Can be used in contexts which busy loop on large number of entries but can
> > > > + * sleep and timing is if no importance to test correctness.
> > > > + */
> > > > +#define XA_BUG_ON_RELAX(xa, x) do {				\
> > > > +	if ((tests_run % 1000) == 0)				\
> > > > +		schedule();					\
> > > > +	XA_BUG_ON(xa, x);					\
> > > > +} while (0)
> > > 
> > > That is awful.  Please don't do that.  You're mixing two completely
> > > unrelated thing into the same macro, which makes no sense.  Not only
> > > that, it's a macro which refers to something in the containing
> > > environment that isn't a paramter to the macro.
> > 
> > I figured you'd puke. Would you prefer I just open code the check on the loop
> > though? I'm sure another alternative is we *not care* about these
> > overloaded systems running the test. What would you prefer?
> 
> OK without any particular preferences outlined this is what I have,
> splitting the two contexts and making the busy loop fix clearer.
> 
> +#define XA_BUSY_LOOP_RELAX(xa, x) do {                         \
> +       if ((i % 1000) == 0)                                    \
> +               schedule();                                     \
> +} while (0)
> +
> +/*
> + * Can be used in contexts which busy loop on large number of entries but can
> + * sleep and timing is if no importance to test correctness.
> + */
> +#define XA_BUG_ON_RELAX(i, xa, x) do {                         \
> +       XA_BUSY_LOOP_RELAX(i);                                  \
> +       XA_BUG_ON(xa, x);                                       \
> +} while (0)

No.  XA_BUG_ON_RELAX is not OK.  Really.

We have a perfectly good system for "relaxing":

        xas_for_each_marked(&xas, page, end, PAGECACHE_TAG_DIRTY) {
                xas_set_mark(&xas, PAGECACHE_TAG_TOWRITE);
                if (++tagged % XA_CHECK_SCHED)
                        continue;

                xas_pause(&xas);
                xas_unlock_irq(&xas);
                cond_resched();
                xas_lock_irq(&xas);
        }