Date:	Mon, 19 Feb 2007 16:20:53 +0530
From:	Balbir Singh <balbir@...ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	linux-kernel@...r.kernel.org, vatsa@...ibm.com,
	ckrm-tech@...ts.sourceforge.net, xemul@...ru, linux-mm@...ck.org,
	menage@...gle.com, svaidy@...ux.vnet.ibm.com, devel@...nvz.org
Subject: Re: [RFC][PATCH][3/4] Add reclaim support

Andrew Morton wrote:
> On Mon, 19 Feb 2007 12:20:42 +0530 Balbir Singh <balbir@...ibm.com> wrote:
> 
>> This patch reclaims pages from a container when the container limit is hit.
>> The executable is oom'ed only when the container it is running in, is overlimit
>> and we could not reclaim any pages belonging to the container
>>
>> A parameter called pushback, controls how much memory is reclaimed when the
>> limit is hit. It should be easy to expose this knob to user space, but
>> currently it is hard coded to 20% of the total limit of the container.
>>
>> isolate_lru_pages() has been modified to isolate pages belonging to a
>> particular container, so that reclaim code will reclaim only container
>> pages. For shared pages, reclaim does not unmap all mappings of the page,
>> it only unmaps those mappings that are over their limit. This ensures
>> that other containers are not penalized while reclaiming shared pages.
>>
>> Parallel reclaim per container is not allowed. Each controller has a wait
>> queue that ensures that only one task per control is running reclaim on
>> that container.
>>
>>
>> ...
>>
>> --- linux-2.6.20/include/linux/rmap.h~memctlr-reclaim-on-limit	2007-02-18 23:29:14.000000000 +0530
>> +++ linux-2.6.20-balbir/include/linux/rmap.h	2007-02-18 23:29:14.000000000 +0530
>> @@ -90,7 +90,15 @@ static inline void page_dup_rmap(struct 
>>   * Called from mm/vmscan.c to handle paging out
>>   */
>>  int page_referenced(struct page *, int is_locked);
>> -int try_to_unmap(struct page *, int ignore_refs);
>> +int try_to_unmap(struct page *, int ignore_refs, void *container);
>> +#ifdef CONFIG_CONTAINER_MEMCTLR
>> +bool page_in_container(struct page *page, struct zone *zone, void *container);
>> +#else
>> +static inline bool page_in_container(struct page *page, struct zone *zone, void *container)
>> +{
>> +	return true;
>> +}
>> +#endif /* CONFIG_CONTAINER_MEMCTLR */
>>  
>>  /*
>>   * Called from mm/filemap_xip.c to unmap empty zero page
>> @@ -118,7 +126,8 @@ int page_mkclean(struct page *);
>>  #define anon_vma_link(vma)	do {} while (0)
>>  
>>  #define page_referenced(page,l) TestClearPageReferenced(page)
>> -#define try_to_unmap(page, refs) SWAP_FAIL
>> +#define try_to_unmap(page, refs, container) SWAP_FAIL
>> +#define page_in_container(page, zone, container)  true
> 
> I spy a compile error.
> 
> The static-inline version looks nicer.
> 


I will compile with the feature turned off and double check. I'll
also convert it to a static inline function.


>>  static inline int page_mkclean(struct page *page)
>>  {
>> diff -puN include/linux/swap.h~memctlr-reclaim-on-limit include/linux/swap.h
>> --- linux-2.6.20/include/linux/swap.h~memctlr-reclaim-on-limit	2007-02-18 23:29:14.000000000 +0530
>> +++ linux-2.6.20-balbir/include/linux/swap.h	2007-02-18 23:29:14.000000000 +0530
>> @@ -188,6 +188,10 @@ extern void swap_setup(void);
>>  /* linux/mm/vmscan.c */
>>  extern unsigned long try_to_free_pages(struct zone **, gfp_t);
>>  extern unsigned long shrink_all_memory(unsigned long nr_pages);
>> +#ifdef CONFIG_CONTAINER_MEMCTLR
>> +extern unsigned long memctlr_shrink_mapped_memory(unsigned long nr_pages,
>> +							void *container);
>> +#endif
> 
> Usually one doesn't need to put ifdefs around the declaration like this. 
> If the function doesn't exist and nobody calls it, we're fine.  If someone
> _does_ call it, we'll find out the error at link-time.
> 

Sure, sounds good. I'll get rid of the #ifdefs.

>>  
>> +/*
>> + * checks if the mm's container and scan control passed container match, if
>> + * so, is the container over it's limit. Returns 1 if the container is above
>> + * its limit.
>> + */
>> +int memctlr_mm_overlimit(struct mm_struct *mm, void *sc_cont)
>> +{
>> +	struct container *cont;
>> +	struct memctlr *mem;
>> +	long usage, limit;
>> +	int ret = 1;
>> +
>> +	if (!sc_cont)
>> +		goto out;
>> +
>> +	read_lock(&mm->container_lock);
>> +	cont = mm->container;
>> +
>> +	/*
>> + 	 * Regular reclaim, let it proceed as usual
>> + 	 */
>> +	if (!sc_cont)
>> +		goto out;
>> +
>> +	ret = 0;
>> +	if (cont != sc_cont)
>> +		goto out;
>> +
>> +	mem = memctlr_from_cont(cont);
>> +	usage = atomic_long_read(&mem->counter.usage);
>> +	limit = atomic_long_read(&mem->counter.limit);
>> +	if (limit && (usage > limit))
>> +		ret = 1;
>> +out:
>> +	read_unlock(&mm->container_lock);
>> +	return ret;
>> +}
> 
> hm, I wonder how much additional lock traffic all this adds.
> 

It's a read_lock() and most of the locks are read_locks
which allow for concurrent access, until the container
changes or goes away

>>  int memctlr_mm_init(struct mm_struct *mm)
>>  {
>>  	mm->counter = kmalloc(sizeof(struct res_counter), GFP_KERNEL);
>> @@ -77,6 +125,46 @@ void memctlr_mm_assign_container(struct 
>>  	write_unlock(&mm->container_lock);
>>  }
>>  
>> +static int memctlr_check_and_reclaim(struct container *cont, long usage,
>> +					long limit)
>> +{
>> +	unsigned long nr_pages = 0;
>> +	unsigned long nr_reclaimed = 0;
>> +	int retries = nr_retries;
>> +	int ret = 1;
>> +	struct memctlr *mem;
>> +
>> +	mem = memctlr_from_cont(cont);
>> +	spin_lock(&mem->lock);
>> +	while ((retries-- > 0) && limit && (usage > limit)) {
>> +		if (mem->reclaim_in_progress) {
>> +			spin_unlock(&mem->lock);
>> +			wait_event(mem->wq, !mem->reclaim_in_progress);
>> +			spin_lock(&mem->lock);
>> +		} else {
>> +			if (!nr_pages)
>> +				nr_pages = (pushback * limit) / 100;
>> +			mem->reclaim_in_progress = true;
>> +			spin_unlock(&mem->lock);
>> +			nr_reclaimed += memctlr_shrink_mapped_memory(nr_pages,
>> +									cont);
>> +			spin_lock(&mem->lock);
>> +			mem->reclaim_in_progress = false;
>> +			wake_up_all(&mem->wq);
>> +		}
>> +		/*
>> + 		 * Resample usage and limit after reclaim
>> + 		 */
>> +		usage = atomic_long_read(&mem->counter.usage);
>> +		limit = atomic_long_read(&mem->counter.limit);
>> +	}
>> +	spin_unlock(&mem->lock);
>> +
>> +	if (limit && (usage > limit))
>> +		ret = 0;
>> +	return ret;
>> +}
> 
> This all looks a bit racy.  And that's common in memory reclaim.  We just
> have to ensure that when the race happens, we do reasonable things.
> 
> I suspect the locking in here could simply be removed.
> 

The locking is mostly to ensure that tasks belonging to the same container
see a consistent value of reclaim_in_progress. I'll see if the locking
can be simplified or simply removed.

>> @@ -66,6 +67,9 @@ struct scan_control {
>>  	int swappiness;
>>  
>>  	int all_unreclaimable;
>> +
>> +	void *container;		/* Used by containers for reclaiming */
>> +					/* pages when the limit is exceeded  */
>>  };
> 
> eww.  Why void*?
> 

I did not want to expose struct container in mm/vmscan.c. An additional
thought was that no matter what container goes in the field would be
useful for reclaim.

>> +#ifdef CONFIG_CONTAINER_MEMCTLR
>> +/*
>> + * Try to free `nr_pages' of memory, system-wide, and return the number of
>> + * freed pages.
>> + * Modelled after shrink_all_memory()
>> + */
>> +unsigned long memctlr_shrink_mapped_memory(unsigned long nr_pages, void *container)
> 
> 80-columns, please.
> 

I'll fix this.

>> +{
>> +	unsigned long ret = 0;
>> +	int pass;
>> +	unsigned long nr_total_scanned = 0;
>> +
>> +	struct scan_control sc = {
>> +		.gfp_mask = GFP_KERNEL,
>> +		.may_swap = 0,
>> +		.swap_cluster_max = nr_pages,
>> +		.may_writepage = 1,
>> +		.swappiness = vm_swappiness,
>> +		.container = container,
>> +		.may_swap = 1,
>> +		.swappiness = 100,
>> +	};
> 
> swappiness got initialised twice.
> 

I should have caught that earlier. Thanks for spotting this.
I'll fix it.

>> +	/*
>> +	 * We try to shrink LRUs in 3 passes:
>> +	 * 0 = Reclaim from inactive_list only
>> +	 * 1 = Reclaim mapped (normal reclaim)
>> +	 * 2 = 2nd pass of type 1
>> +	 */
>> +	for (pass = 0; pass < 3; pass++) {
>> +		int prio;
>> +
>> +		for (prio = DEF_PRIORITY; prio >= 0; prio--) {
>> +			unsigned long nr_to_scan = nr_pages - ret;
>> +
>> +			sc.nr_scanned = 0;
>> +			ret += shrink_all_zones(nr_to_scan, prio,
>> +						pass, 1, &sc);
>> +			if (ret >= nr_pages)
>> +				goto out;
>> +
>> +			nr_total_scanned += sc.nr_scanned;
>> +			if (sc.nr_scanned && prio < DEF_PRIORITY - 2)
>> +				congestion_wait(WRITE, HZ / 10);
>> +		}
>> +	}
>> +out:
>> +	return ret;
>> +}
>> +#endif
> 


-- 
	Warm Regards,
	Balbir Singh
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