linux-kernel - Re: [PATCH v2 2/2] mm/vmalloc: Print a warning message first on failure

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Message-ID: <20210509200519.GA3016@pc638.lan>
Date:   Sun, 9 May 2021 22:05:19 +0200
From:   Uladzislau Rezki <urezki@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     "Uladzislau Rezki (Sony)" <urezki@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Mel Gorman <mgorman@...e.de>, Hillf Danton <hdanton@...a.com>,
        Michal Hocko <mhocko@...e.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v2 2/2] mm/vmalloc: Print a warning message first on
 failure

On Sun, May 09, 2021 at 08:47:12PM +0100, Matthew Wilcox wrote:
> On Sun, May 09, 2021 at 09:38:44PM +0200, Uladzislau Rezki (Sony) wrote:
> >  export KBUILD_USERCFLAGS := -Wall -Wmissing-prototypes -Wstrict-prototypes \
> > -			      -O2 -fomit-frame-pointer -std=gnu89
> > +			      -O0 -g -fomit-frame-pointer -std=gnu89
> 
> You clearly didn't intend to submit this portion ...
> 
I sent a v3 that does not include it. That was added accidentally.

> > +++ b/mm/vmalloc.c
> > @@ -2781,11 +2781,11 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
> >  	}
> >  
> >  	if (!area->pages) {
> > -		free_vm_area(area);
> >  		warn_alloc(gfp_mask, NULL,
> >  			   "vmalloc size %lu allocation failure: "
> >  			   "page array size %lu allocation failed",
> >  			   nr_small_pages * PAGE_SIZE, array_size);
> > +		free_vm_area(area);
> >  		return NULL;
> >  	}
> 
> I think this is a bad idea.  We're clearly low on memory (a memory
> allocation just failed).  We should free the memory we have allocated
> to improve the chances of the warning message making it out.
Not sure if i fully follow you here. We do free the memory. The intention
was to print a warning message first because, if, potentially, the
free_vm_area(area) also does some prints it would be a bit messy from the
point what has been broken first.

So, could you please clarify what was your concern?

--
Vlad Rezki