linux-kernel - Re: [PATCH 2/3] zram: try vmalloc() after kmalloc()

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Message-ID: <20151124061258.GJ705@swordfish>
Date:	Tue, 24 Nov 2015 15:12:58 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Kyeongdon Kim <kyeongdon.kim@....com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH 2/3] zram: try vmalloc() after kmalloc()

[..]
>  static void *zcomp_lz4_create(void)
>  {
> -       return kzalloc(LZ4_MEM_COMPRESS, GFP_KERNEL);
> +       void *ret;
> +
> +       /*
> +        * This function could be called in swapout/fs write path
> +        * so we couldn't use GFP_FS|IO. And it assumes we already
> +        * have at least one stream in zram initialization so we
> +        * don't do best effort to allocate more stream in here.
> +        * A default stream will work well without further multiple
> +        * stream. That's why we use  __GFP_NORETRY|NOWARN|NOMEMALLOC.
> +        */
> +       ret = kzalloc(LZ4_MEM_COMPRESS,
> +                       __GFP_NORETRY|__GFP_NOWARN|__GFP_NOMEMALLOC);
> +       if (!ret)
> +               ret = __vmalloc(LZ4_MEM_COMPRESS,
> +                                       __GFP_NORETRY|__GFP_NOWARN|
> +                                       __GFP_NOMEMALLOC|__GFP_ZERO,
> +                                       PAGE_KERNEL);
> +       return ret;
>  }
[..]

so this change is still questionable. is there a real value in having
a vmalloc() fallback in the middle of allocations sequence:

	zstrm = kmalloc(sizeof(*zstrm), GFP_NOIO);
		^^^ ok, can fail here

	zstrm->zstrm->private = comp->backend->create();
				^^^ kzalloc() and vmalloc() fallback ??

	zstrm->buffer = (void *)__get_free_pages(GFP_NOIO | __GFP_ZERO, 1);
		^^^ can fail here again.

can you please comment on this?


and I'd prefer it to be a bit different -- use likely path first and
avoid an assignment in unlikely path.
... and add GFP_NOIO to both kzalloc() and __vmalloc().

and there is no __GFP_HIGHMEM in __vmalloc() call?

something like this:

---


	ret = kzalloc(LZ4_MEM_COMPRESS, GFP_NOIO | __GFP_NORETRY |
					__GFP_NOWARN | __GFP_NOMEMALLOC);
	if (ret)
		return ret;

	return __vmalloc(LZ4_MEM_COMPRESS,
			GFP_NOIO | __GFP_NOWARN | __GFP_HIGHMEM | __GFP_ZERO,
			PAGE_KERNEL);


	-ss
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