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

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Message-ID: <20250506133706.GA29215@lst.de>
Date: Tue, 6 May 2025 15:37:06 +0200
From: Christoph Hellwig <hch@....de>
To: Herbert Xu <herbert@...dor.apana.org.au>
Cc: Yosry Ahmed <yosry.ahmed@...ux.dev>,
	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 09:27:49PM +0800, Herbert Xu wrote:
> 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.

You absolutely can and lots of code does.