linux-kernel - Re: [PATCH 2/4] mm/vmap: preload a CPU with one object for split purpose

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Date:   Fri, 24 May 2019 16:14:44 +0200
From:   Uladzislau Rezki <urezki@...il.com>
To:     Hillf Danton <hdanton@...a.com>
Cc:     "Uladzislau Rezki (Sony)" <urezki@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>, Michal Hocko <mhocko@...e.com>,
        Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Garnier <thgarnie@...gle.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joelaf@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...e.hu>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH 2/4] mm/vmap: preload a CPU with one object for split
 purpose

On Fri, May 24, 2019 at 06:33:16PM +0800, Hillf Danton wrote:
> 
> On Wed, 22 May 2019 17:09:37 +0200 Uladzislau Rezki (Sony) wrote:
> >  /*
> > + * Preload this CPU with one extra vmap_area object to ensure
> > + * that we have it available when fit type of free area is
> > + * NE_FIT_TYPE.
> > + *
> > + * The preload is done in non-atomic context thus, it allows us
> > + * to use more permissive allocation masks, therefore to be more
> > + * stable under low memory condition and high memory pressure.
> > + *
> > + * If success, it returns zero with preemption disabled. In case
> > + * of error, (-ENOMEM) is returned with preemption not disabled.
> > + * Note it has to be paired with alloc_vmap_area_preload_end().
> > + */
> > +static void
> > +ne_fit_preload(int *preloaded)
> > +{
> > +	preempt_disable();
> > +
> > +	if (!__this_cpu_read(ne_fit_preload_node)) {
> > +		struct vmap_area *node;
> > +
> > +		preempt_enable();
> > +		node = kmem_cache_alloc(vmap_area_cachep, GFP_KERNEL);
> 
> Alternatively, can you please take another look at the upside to use
> the memory node parameter in alloc_vmap_area() for allocating va slab,
> given that this preload, unlike adjust_va_to_fit_type() is invoked
> with the vmap_area_lock not aquired?
> 
Agree. That makes sense. I will upload the v2 where fix all comments.

Thank you!

--
Vlad Rezki