linux-kernel - Re: [PATCH 3/5] mm/vmalloc.c: optimize code in decay_va_pool

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Message-ID: <aAEp8R0GcKCXtMwG@pc636>
Date: Thu, 17 Apr 2025 18:18:57 +0200
From: Uladzislau Rezki <urezki@...il.com>
To: Baoquan He <bhe@...hat.com>
Cc: Uladzislau Rezki <urezki@...il.com>, linux-mm@...ck.org,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] mm/vmalloc.c: optimize code in decay_va_pool_node()
 a little bit

On Thu, Apr 17, 2025 at 10:51:44AM +0800, Baoquan He wrote:
> On 04/16/25 at 03:50pm, Uladzislau Rezki wrote:
> > On Tue, Apr 15, 2025 at 10:39:50AM +0800, Baoquan He wrote:
> > > When purge lazily freed vmap areas, VA stored in vn->pool[] will also be
> > > taken away into free vmap tree partially or completely accordingly, that
> > > is done in decay_va_pool_node(). When doing that, for each pool of node,
> > > the whole list is detached from the pool for handling. At this time,
> > > that pool is empty. It's not necessary to update the pool size each time
> > > when one VA is removed and addded into free vmap tree.
> > > 
> > > Here change code to update the pool size when attaching the pool back.
> > > 
> > > Signed-off-by: Baoquan He <bhe@...hat.com>
> > > ---
> > >  mm/vmalloc.c | 23 +++++++++++------------
> > >  1 file changed, 11 insertions(+), 12 deletions(-)
> > > 
> > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > > index 488d69b56765..bf735c890878 100644
> > > --- a/mm/vmalloc.c
> > > +++ b/mm/vmalloc.c
> > > @@ -2150,7 +2150,7 @@ decay_va_pool_node(struct vmap_node *vn, bool full_decay)
> > >  	LIST_HEAD(decay_list);
> > >  	struct rb_root decay_root = RB_ROOT;
> > >  	struct vmap_area *va, *nva;
> > > -	unsigned long n_decay;
> > > +	unsigned long n_decay, len;
> > >  	int i;
> > >  
> > >  	for (i = 0; i < MAX_VA_SIZE_PAGES; i++) {
> > > @@ -2164,22 +2164,20 @@ decay_va_pool_node(struct vmap_node *vn, bool full_decay)
> > >  		list_replace_init(&vn->pool[i].head, &tmp_list);
> > >  		spin_unlock(&vn->pool_lock);
> > >  
> > > -		if (full_decay)
> > > -			WRITE_ONCE(vn->pool[i].len, 0);
> > > +		len = n_decay = vn->pool[i].len;
> > > +		WRITE_ONCE(vn->pool[i].len, 0);
> > >  
> > >  		/* Decay a pool by ~25% out of left objects. */
> > > -		n_decay = vn->pool[i].len >> 2;
> > > +		if (!full_decay)
> > > +			n_decay >>= 2;
> > > +		len -= n_decay;
> > >  
> > >  		list_for_each_entry_safe(va, nva, &tmp_list, list) {
> > > +			if (!n_decay)
> > > +				break;
> > >  			list_del_init(&va->list);
> > >  			merge_or_add_vmap_area(va, &decay_root, &decay_list);
> > > -
> > > -			if (!full_decay) {
> > > -				WRITE_ONCE(vn->pool[i].len, vn->pool[i].len - 1);
> > > -
> > > -				if (!--n_decay)
> > > -					break;
> > > -			}
> > > +			n_decay--;
> > >  		}
> > >  
> > >  		/*
> > > @@ -2188,9 +2186,10 @@ decay_va_pool_node(struct vmap_node *vn, bool full_decay)
> > >  		 * can populate the pool therefore a simple list replace
> > >  		 * operation takes place here.
> > >  		 */
> > > -		if (!full_decay && !list_empty(&tmp_list)) {
> > > +		if (!list_empty(&tmp_list)) {
> > >  			spin_lock(&vn->pool_lock);
> > >  			list_replace_init(&tmp_list, &vn->pool[i].head);
> > > +			vn->pool[i].len = len;
> > >  			spin_unlock(&vn->pool_lock);
> > >  		}
> > >  	}
> > > -- 
> > > 2.41.0
> > > 
> > Which Linux version this patch is based on? I can not apply it.
> 
> I can apply them on the latest mainline kernel, next/master and
> mm-new branch of akpm/mm.git. I checked just now.
> 
Sounds good.

--
Uladzislau Rezki