linux-kernel - Re: [PATCHv1 3/6] zsmalloc: make zspage lock preemptible

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Message-ID: <3oxqvpghezesl6nj474v3xchpseeavc6p3u752yaxswpfmcqxd@ohdx62ahgle5>
Date: Thu, 30 Jan 2025 12:22:08 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Uros Bizjak <ubizjak@...il.com>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, Minchan Kim <minchan@...nel.org>, 
	Johannes Weiner <hannes@...xchg.org>, Yosry Ahmed <yosry.ahmed@...ux.dev>, 
	Nhat Pham <nphamcs@...il.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv1 3/6] zsmalloc: make zspage lock preemptible

On (25/01/29 16:22), Uros Bizjak wrote:
> > +static void zspage_read_lock(struct zspage *zspage)
> > +{
> > +	atomic_t *lock = &zspage->lock;
> > +	int old;
> > +
> > +	while (1) {
> > +		old = atomic_read(lock);
> > +		if (old == ZS_PAGE_WRLOCKED) {
> > +			cpu_relax();
> > +			continue;
> > +		}
> > +
> > +		if (atomic_try_cmpxchg(lock, &old, old + 1))
> > +			return;
> > +
> > +		cpu_relax();
> > +	}
> > +}

[..]

> Based on the above, cpu_relax() should be removed from the loop, which
> becomes:
> 
> {
>         atomic_t *lock = &zspage->lock;
>         int old = atomic_read(lock);
> 
>         do {
>                 if (old == ZS_PAGE_WRLOCKED) {
>                         cpu_relax();
>                         old = atomic_read(lock);
>                         continue;
>                 }
> 
>         } while (!atomic_try_cmpxchg(lock, &old, old + 1));
>  }

Ack.

> > +static int zspage_try_write_lock(struct zspage *zspage)
> 
> This function can be declared as bool, returning true/false.

Ack.  Thank you.