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Date:   Sat, 18 Apr 2020 13:15:09 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        Manfred Spraul <manfred@colorfullife.com>,
        Davidlohr Bueso <dave@stgolabs.net>
Subject: Re: [PATCH] ipc: Convert ipcs_idr to XArray
Message-Id: <20200418131509.fb3c19bf450d618be797c030@linux-foundation.org>
In-Reply-To: <20200326151418.27545-1-willy@infradead.org>
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On Thu, 26 Mar 2020 08:14:18 -0700 Matthew Wilcox <willy@infradead.org> wrote:

> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> 
> The XArray has better loops than the IDR has, removing the need to
> open-code them.  We also don't need to call idr_destroy() any more.
> Allocating the ID is a little tricky due to needing to get 'seq'
> correct.  Open-code a variant of __xa_alloc() which lets us set the
> ID and the seq before depositing the pointer in the array.

hm, this goes rather deep.  Manfred & Davidlohr, are you able to run
this through some testing?

>
> ...
>
> --- a/ipc/util.c
> +++ b/ipc/util.c
> @@ -104,12 +104,20 @@ static const struct rhashtable_params ipc_kht_params = {
>  	.automatic_shrinking	= true,
>  };
>  
> +#ifdef CONFIG_CHECKPOINT_RESTORE

The code grew a few additional CONFIG_CHECKPOINT_RESTORE ifdefs. 
What's going on here?  Why is CRIU special in ipc/?

> +#define set_restore_id(ids, x)	ids->restore_id = x
> +#define get_restore_id(ids)	ids->restore_id
> +#else
> +#define set_restore_id(ids, x)	do { } while (0)
> +#define get_restore_id(ids)	(-1)
> +#endif

Well these are ugly.  Can't all this be done in C?

>
> ...
>