linux-kernel - Re: [PATCH v2 09/16] rcu/tree: Maintain separate array for vmalloc ptrs

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Date:   Thu, 18 Jun 2020 11:37:51 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Uladzislau Rezki <urezki@...il.com>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Joel Fernandes <joel@...lfernandes.org>,
        RCU <rcu@...r.kernel.org>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>
Subject: Re: [PATCH v2 09/16] rcu/tree: Maintain separate array for vmalloc
 ptrs

On Thu, Jun 18, 2020 at 08:23:33PM +0200, Uladzislau Rezki wrote:
> > +void vfree_bulk(size_t count, void **addrs)
> > +{
> > +	unsigned int i;
> > +
> > +	BUG_ON(in_nmi());
> > +	might_sleep_if(!in_interrupt());
> > +
> > +	for (i = 0; i < count; i++) {
> > +		void *addr = addrs[i];
> > +		kmemleak_free(addr);
> > +		if (addr)
> > +			__vfree(addr);
> > +	}
> > +}
> > +EXPORT_SYMBOL(vfree_bulk);
> > +
> >
> Can we just do addrs[i] all over the loop?
> 
> Also, we can just call vfree() instead that has all checking we
> need: NMI, kmemleak, might_sleep.

Of course we _can_.  But would we want to?  This way, we only do these
checks once instead of once per pointer, which is rather the point
of batching.

I might actually go further and hoist the in_interrupt() check into
this function ... I suspect the RCU code always runs in_interrupt()
and so we always call vfree_deferred().