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

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Message-ID: <b42gpp5qsa4j22ai2v4rwwkjhvfbcbf3lcnjoccz7xeidae5c7@ot2ocric3qzs>
Date: Wed, 7 May 2025 15:08:08 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
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>, Igor Belousov <igor.b@...dev.am>, 
	Herbert Xu <herbert@...dor.apana.org.au>, Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [PATCH] mm/zblock: use vmalloc for page allocations

On (25/05/07 14:57), Sergey Senozhatsky wrote:
> On (25/05/06 13:13), Yosry Ahmed wrote:
> > If we can use vmalloc for zblock, then we can probably also use vmalloc
> > in zsmalloc and get rid of the chaining logic completely. This would
> > make zsmalloc simpler and closer to zblock in that regard.
> > 
> > Sergey, WDYT?
> 
> This sounds interesting.  We might get rid of lots of memcpy()
> in object read/write paths, and so on.  I don't know if 0-order
> chaining was the only option for zsmalloc, or just happened to
> be the first one.

I assume we might have problems with zspage release path.  vfree()
should break .swap_slot_free_notify, as far as I can see.
.swap_slot_free_notify is called under swap-cluster spin-lock,
so if we free the last object in the zspage we cannot immediately
free that zspage, because vfree() might_sleep().