linux-kernel - Re: [PATCH] nfsd: more robust allocation failure handling in nfsd_reply_cache

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Date:   Thu, 20 Oct 2016 09:09:40 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Bruce Fields <bfields@...ldses.org>
Cc:     Jeff Layton <jlayton@...hat.com>,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Olaf Hering <olaf@...fle.de>
Subject: Re: [PATCH] nfsd: more robust allocation failure handling in nfsd_reply_cache_init

On Thu, Oct 20, 2016 at 8:52 AM, Bruce Fields <bfields@...ldses.org> wrote:
>
> Jeff was also wondering whether we could instead just allocate this with
> vmalloc--is there any drawback?  We only allocate this on nfsd startup,
> so if the only drawback is the allocation itself being expensive then
> that's no big deal.

vmalloc is ok. Generally if it's *usually* a small allocation, the
best pattern tends to be to first try to kmalloc (of get_free_pages())
using __GFP_NORETRY | __GFP_NOWARN, and then fall back on vmalloc().
That way you don't end up doing vmalloc's for things that really don't
need it.

If you do that, we have a "kvfree()" helper that is "free either
kmalloc or vmalloc area", so you don't have to track after-the-fact
which one you did.

               Linus