linux-kernel - Re: [PATCH 1/2] mm: swap_cgroup: allocate swap

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Message-ID: <ZzfPS_YFeWVhySQJ@google.com>
Date: Fri, 15 Nov 2024 22:46:35 +0000
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Michal Hocko <mhocko@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH 1/2] mm: swap_cgroup: allocate swap_cgroup map using
 vcalloc()

On Fri, Nov 15, 2024 at 12:17:43PM -0800, Shakeel Butt wrote:
> On Fri, Nov 15, 2024 at 07:02:28PM +0000, Roman Gushchin wrote:
> > Currently swap_cgroup's map is constructed as a vmalloc()'s-based
> > array of pointers to individual struct pages. This brings an
> > unnecessary complexity into the code.
> > 
> > This patch turns the swap_cgroup's map into a single space
> > allocated by vcalloc().
> > 
> > Signed-off-by: Roman Gushchin <roman.gushchin@...ux.dev>
> 
> Acked-by: Shakeel Butt <shakeel.butt@...ux.dev>

Thank you for reviewing the patchset!

> 
> [...]
> > @@ -215,19 +169,8 @@ void swap_cgroup_swapoff(int type)
> >  	mutex_lock(&swap_cgroup_mutex);
> >  	ctrl = &swap_cgroup_ctrl[type];
> >  	map = ctrl->map;
> > -	length = ctrl->length;
> >  	ctrl->map = NULL;
> > -	ctrl->length = 0;
> >  	mutex_unlock(&swap_cgroup_mutex);
> >  
> > -	if (map) {
> > -		for (i = 0; i < length; i++) {
> > -			struct page *page = map[i];
> > -			if (page)
> > -				__free_page(page);
> > -			if (!(i % SWAP_CLUSTER_MAX))
> > -				cond_resched();
> > -		}
> > -		vfree(map);
> > -	}
> > +	kvfree(map);
> 
> Any reason to use kvfree() instead of just vfree()?

No, you're right, vfree() is a better choice here.

Andrew, do you prefer a v2 or it's easier to master a fix-up?

Thank you!