linux-kernel - Re: [PATCH] mm/zblock: use vmalloc for page allocations

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Message-ID: <aBoOVajBDXkFNUBI@gondor.apana.org.au>
Date: Tue, 6 May 2025 21:27:49 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Yosry Ahmed <yosry.ahmed@...ux.dev>
Cc: Vitaly Wool <vitaly.wool@...sulko.se>, linux-mm@...ck.org,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Nhat Pham <nphamcs@...il.com>,
	Shakeel Butt <shakeel.butt@...ux.dev>,
	Johannes Weiner <hannes@...xchg.org>,
	Minchan Kim <minchan@...nel.org>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Igor Belousov <igor.b@...dev.am>, Christoph Hellwig <hch@....de>
Subject: Re: [PATCH] mm/zblock: use vmalloc for page allocations

On Tue, May 06, 2025 at 01:13:17PM +0000, Yosry Ahmed wrote:
>
> Keep in mind that zswap_decompress() will always do an extra copy if the
> address returned by zpool_obj_read_begin() is a vmalloc address. To
> avoid this we need to enlighten the scatterlist API to work with vmalloc
> addresses.
> 
> (CC'ing Herbert as he was looking into this)

acomp now supports linear addresses so vmalloc can be sent through
directly.  It will fail if you use hardware offload though since
you can't DMA directly to vmalloc virtual addresses.

If you wish to support hardware offload, then you'll need to break
the vmalloc memory down page-by-page to create an SG list.

Adding Christoph to the cc list in case he knows of any updates in
this area (using vmalloc memory with DMA).

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt