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Date: Mon, 4 Feb 2002 17:20:34 -0600
From: Ken Brownfield <brownfld@irridia.com>
To: Ed Tomlinson <tomlins@cam.org>
Cc: Marcelo Tosatti <marcelo@conectiva.com.br>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] improved free page accounting
Message-ID: <20020204172034.B14297@asooo.flowerfire.com>
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In-Reply-To: <20020202161912.D41D615CF1@oscar.casa.dyndns.org>; from tomlins@cam.org on Sat, Feb 02, 2002 at 11:19:12AM -0500
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Yes -- I noticed before when I was doing primitive hacking on this code
that these functions don't contribute to nr_pages, which seemed to
result in over-delayed purging of the caches.  I would think that having
these functions contribute to the shrink_caches nr_pages "heuristic"
could help, which is one thing that attracts me to rmap.

It would be interesting to hear Andrea's take on this, since something
like this with appropriate tuning could be a useful addition to 10_vm,
which is due to be merged in mainline any day now, right? ;-)
-- 
Ken.
brownfld@irridia.com


On Sat, Feb 02, 2002 at 11:19:12AM -0500, Ed Tomlinson wrote:
| The following patch improves the free page accounting.  It does 
| this by creating variants of the shrink functions used by the
| inode, dentry, dquota caches that return the number of pages 
| they free.  Current interfaces are not modified.  A variant
| of this code is in the rmap patch and was reduced the number 
| of false oom triggers.
| 
| I have been running versions of this since 2.4.14.
| 
| Patch is against 2.4.17pre7
| 
| Comments,
| Ed Tomlinson
| 
| --- linux/fs/inode.c.orig	Sat Jan  5 17:35:17 2002
| +++ linux/fs/inode.c	Sat Jan  5 17:36:06 2002
| @@ -725,8 +725,7 @@
|  	count = inodes_stat.nr_unused / priority;
|  
|  	prune_icache(count);
| -	kmem_cache_shrink(inode_cachep);
| -	return 0;
| +	return kmem_cache_shrink_nr(inode_cachep);
|  }
|  
|  /*
| --- linux/fs/dcache.c.orig	Sat Jan  5 17:37:02 2002
| +++ linux/fs/dcache.c	Sat Jan  5 17:37:57 2002
| @@ -568,8 +568,7 @@
|  	count = dentry_stat.nr_unused / priority;
|  
|  	prune_dcache(count);
| -	kmem_cache_shrink(dentry_cache);
| -	return 0;
| +	return kmem_cache_shrink_nr(dentry_cache);
|  }
|  
|  #define NAME_ALLOC_LEN(len)	((len+16) & ~15)
| --- linux/fs/dquot.c.orig	Sat Jan  5 17:38:21 2002
| +++ linux/fs/dquot.c	Sat Jan  5 17:38:57 2002
| @@ -413,8 +413,7 @@
|  	lock_kernel();
|  	prune_dqcache(nr_free_dquots / (priority + 1));
|  	unlock_kernel();
| -	kmem_cache_shrink(dquot_cachep);
| -	return 0;
| +	return kmem_cache_shrink_nr(dquot_cachep);
|  }
|  
|  /* NOTE: If you change this function please check whether dqput_blocks() works right... */
| --- linux/include/linux/slab.h.orig	Sat Jan  5 17:27:13 2002
| +++ linux/include/linux/slab.h	Sat Jan  5 17:27:49 2002
| @@ -55,6 +55,7 @@
|  				       void (*)(void *, kmem_cache_t *, unsigned long));
|  extern int kmem_cache_destroy(kmem_cache_t *);
|  extern int kmem_cache_shrink(kmem_cache_t *);
| +extern int kmem_cache_shrink_nr(kmem_cache_t *);
|  extern void *kmem_cache_alloc(kmem_cache_t *, int);
|  extern void kmem_cache_free(kmem_cache_t *, void *);
|  
| --- linux/mm/slab.c.orig	Sat Jan  5 15:06:40 2002
| +++ linux/mm/slab.c	Sat Jan  5 18:54:40 2002
| @@ -911,34 +911,45 @@
|  #define drain_cpu_caches(cachep)	do { } while (0)
|  #endif
|  
| +/**
| + * Called with the &cachep->spinlock held, returns number of slabs released
| + */
| +static int __kmem_cache_shrink_locked(kmem_cache_t *cachep)
| +{
| +        slab_t *slabp;
| +        int ret = 0;
| +
| +        /* If the cache is growing, stop shrinking. */
| +        while (!cachep->growing) {
| +                struct list_head *p;
| +
| +                p = cachep->slabs_free.prev;
| +                if (p == &cachep->slabs_free)
| +                        break;
| +
| +                slabp = list_entry(cachep->slabs_free.prev, slab_t, list);
| +#if DEBUG
| +                if (slabp->inuse)
| +                        BUG();
| +#endif
| +                list_del(&slabp->list);
| +
| +                spin_unlock_irq(&cachep->spinlock);
| +                kmem_slab_destroy(cachep, slabp);
| +		ret++;
| +                spin_lock_irq(&cachep->spinlock);
| +        }
| +        return ret;
| +}
| +
|  static int __kmem_cache_shrink(kmem_cache_t *cachep)
|  {
| -	slab_t *slabp;
|  	int ret;
|  
|  	drain_cpu_caches(cachep);
|  
|  	spin_lock_irq(&cachep->spinlock);
| -
| -	/* If the cache is growing, stop shrinking. */
| -	while (!cachep->growing) {
| -		struct list_head *p;
| -
| -		p = cachep->slabs_free.prev;
| -		if (p == &cachep->slabs_free)
| -			break;
| -
| -		slabp = list_entry(cachep->slabs_free.prev, slab_t, list);
| -#if DEBUG
| -		if (slabp->inuse)
| -			BUG();
| -#endif
| -		list_del(&slabp->list);
| -
| -		spin_unlock_irq(&cachep->spinlock);
| -		kmem_slab_destroy(cachep, slabp);
| -		spin_lock_irq(&cachep->spinlock);
| -	}
| +	__kmem_cache_shrink_locked(cachep);
|  	ret = !list_empty(&cachep->slabs_full) || !list_empty(&cachep->slabs_partial);
|  	spin_unlock_irq(&cachep->spinlock);
|  	return ret;
| @@ -957,6 +968,24 @@
|  		BUG();
|  
|  	return __kmem_cache_shrink(cachep);
| +}
| +
| +/**
| + * kmem_cache_shrink_nr - Shrink a cache returning pages released
| + */
| +int kmem_cache_shrink_nr(kmem_cache_t *cachep)
| +{
| +        int ret;
| +
| +        if (!cachep || in_interrupt() || !is_chained_kmem_cache(cachep))
| +                BUG();
| +
| +	drain_cpu_caches(cachep);
| +
| +	spin_lock_irq(&cachep->spinlock);
| +	ret = __kmem_cache_shrink_locked(cachep);
| +	spin_unlock_irq(&cachep->spinlock);
| +	return ret<<(cachep->gfporder);
|  }
|  
|  /**
| --- linux/mm/vmscan.c.orig	Sun Jan 13 08:47:58 2002
| +++ linux/mm/vmscan.c	Sun Jan 13 08:48:27 2002
| @@ -567,7 +567,6 @@
|  	if (nr_pages <= 0)
|  		return 0;
|  
| -	nr_pages = chunk_size;
|  	/* try to keep the active list 2/3 of the size of the cache */
|  	ratio = (unsigned long) nr_pages * nr_active_pages / ((nr_inactive_pages + 1) * 2);
|  	refill_inactive(ratio);
| @@ -576,13 +575,13 @@
|  	if (nr_pages <= 0)
|  		return 0;
|  
| -	shrink_dcache_memory(priority, gfp_mask);
| -	shrink_icache_memory(priority, gfp_mask);
| +	nr_pages -= shrink_dcache_memory(priority, gfp_mask);
| +	nr_pages -= shrink_icache_memory(priority, gfp_mask);
|  #ifdef CONFIG_QUOTA
| -	shrink_dqcache_memory(DEF_PRIORITY, gfp_mask);
| +	nr_pages -= shrink_dqcache_memory(DEF_PRIORITY, gfp_mask);
|  #endif
|  
| -	return nr_pages;
| +	return (nr_pages<=0 ? 0 : nr_pages);
|  }
|  
|  int try_to_free_pages(zone_t *classzone, unsigned int gfp_mask, unsigned int order)
| -
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