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

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Message-ID: <20210509212641.GA3220@pc638.lan>
Date:   Sun, 9 May 2021 23:26:41 +0200
From:   Uladzislau Rezki <urezki@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Uladzislau Rezki <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 09:18:46PM +0100, Matthew Wilcox wrote:
> On Sun, May 09, 2021 at 10:05:19PM +0200, Uladzislau Rezki wrote:
> > On Sun, May 09, 2021 at 08:47:12PM +0100, Matthew Wilcox wrote:
> > > > +++ 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?
> 
> We may need to allocate memory in order to emit the error message.
>
> Your commit message didn't mention the potential confusion, and I think
> that is worth adding for a v4.
I agree that the commit message should be updated in regard of potential
confusion, because it was the main intention of this patch.

I will upload a v4 tomorrow.

--
Vlad Rezki