Re: [PATCH] nfsd: more robust allocation failure handling in nfsd_reply_cache_init

[Linus Torvalds]

On Thu, Oct 20, 2016 at 8:52 AM, Bruce Fields <bfields@xxxxxxxxxxxx> 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