linux-kernel - Re: [PATCH] mm:memcg: add __GFP_NOWARN in __memcg_schedule_kmem_cache

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Date:   Tue, 17 Apr 2018 21:16:42 -0700 (PDT)
From:   David Rientjes <rientjes@...gle.com>
To:     Matthew Wilcox <willy@...radead.org>
cc:     Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>
Subject: Re: [PATCH] mm:memcg: add __GFP_NOWARN in
 __memcg_schedule_kmem_cache_create

On Tue, 17 Apr 2018, Matthew Wilcox wrote:

> Not arguing against this patch.  But how many places do we want to use
> GFP_NOWAIT without __GFP_NOWARN?  Not many, and the few which do do this
> seem like they simply haven't added it yet.  Maybe this would be a good idea?
> 
> -#define GFP_NOWAIT      (__GFP_KSWAPD_RECLAIM)
> +#define GFP_NOWAIT      (__GFP_KSWAPD_RECLAIM | __GFP_NOWARN)
> 

I don't think that's a good idea, slab allocators use GFP_NOWAIT during 
init, for example, followed up with a BUG_ON() if it fails.  With an 
implicit __GFP_NOWARN we wouldn't be able to see the state of memory when 
it crashes (likely memory that wasn't freed to the allocator).  I think 
whether the allocation failure should trigger a warning is up to the 
caller.