linux-kernel - Re: [PATCH 1/1] mm/vmalloc: remove preempt

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Date:   Fri, 11 Oct 2019 16:55:15 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Uladzislau Rezki <urezki@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Daniel Wagner <dwagner@...e.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Hillf Danton <hdanton@...a.com>,
        Michal Hocko <mhocko@...e.com>,
        Matthew Wilcox <willy@...radead.org>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>
Subject: Re: [PATCH 1/1] mm/vmalloc: remove preempt_disable/enable when do
 preloading

On Thu, 10 Oct 2019 17:17:49 +0200 Uladzislau Rezki <urezki@...il.com> wrote:

> > > : 	 * The preload is done in non-atomic context, thus it allows us
> > > : 	 * to use more permissive allocation masks to be more stable under
> > > : 	 * low memory condition and high memory pressure.
> > > : 	 *
> > > : 	 * Even if it fails we do not really care about that. Just proceed
> > > : 	 * as it is. "overflow" path will refill the cache we allocate from.
> > > : 	 */
> > > : 	if (!this_cpu_read(ne_fit_preload_node)) {
> > > 
> > > Readability nit: local `pva' should be defined here, rather than having
> > > function-wide scope.
> > > 
> > > : 		pva = kmem_cache_alloc_node(vmap_area_cachep, GFP_KERNEL, node);
> > > 
> > > Why doesn't this honour gfp_mask?  If it's not a bug, please add
> > > comment explaining this.
> > > 
> But there is a comment, if understand you correctly:
> 
> <snip>
> * Even if it fails we do not really care about that. Just proceed
> * as it is. "overflow" path will refill the cache we allocate from.
> <snip>

My point is that the alloc_vmap_area() caller passed us a gfp_t but
this code ignores it, as does adjust_va_to_fit_type().  These *look*
like potential bugs.  If not, they should be commented so they don't
look like bugs any more ;)