[Devel] Re: [ckrm-tech] [RFC][PATCH][2/4] Add RSS accounting and control

[Balbir Singh]

Andrew Morton wrote:
> On Mon, 19 Feb 2007 12:20:34 +0530 Balbir Singh <balbir at in.ibm.com> wrote:
> 
>> This patch adds the basic accounting hooks to account for pages allocated
>> into the RSS of a process. Accounting is maintained at two levels, in
>> the mm_struct of each task and in the memory controller data structure
>> associated with each node in the container.
>>
>> When the limit specified for the container is exceeded, the task is killed.
>> RSS accounting is consistent with the current definition of RSS in the
>> kernel. Shared pages are accounted into the RSS of each process as is
>> done in the kernel currently. The code is flexible in that it can be easily
>> modified to work with any definition of RSS.
>>
>> ..
>>
>> +static inline int memctlr_mm_init(struct mm_struct *mm)
>> +{
>> +	return 0;
>> +}
> 
> So it returns zero on success.  OK.
> 

Oops. it should return 1 on success.

>> --- linux-2.6.20/kernel/fork.c~memctlr-acct	2007-02-18 22:55:50.000000000 +0530
>> +++ linux-2.6.20-balbir/kernel/fork.c	2007-02-18 22:55:50.000000000 +0530
>> @@ -50,6 +50,7 @@
>>  #include <linux/taskstats_kern.h>
>>  #include <linux/random.h>
>>  #include <linux/numtasks.h>
>> +#include <linux/memctlr.h>
>>  
>>  #include <asm/pgtable.h>
>>  #include <asm/pgalloc.h>
>> @@ -342,10 +343,15 @@ static struct mm_struct * mm_init(struct
>>  	mm->free_area_cache = TASK_UNMAPPED_BASE;
>>  	mm->cached_hole_size = ~0UL;
>>  
>> +	if (!memctlr_mm_init(mm))
>> +		goto err;
>> +
> 
> But here we treat zero as an error?
> 

It's a BUG, I'll fix it.


>>  	if (likely(!mm_alloc_pgd(mm))) {
>>  		mm->def_flags = 0;
>>  		return mm;
>>  	}
>> +
>> +err:
>>  	free_mm(mm);
>>  	return NULL;
>>  }
>>
>> ...
>>
>> +int memctlr_mm_init(struct mm_struct *mm)
>> +{
>> +	mm->counter = kmalloc(sizeof(struct res_counter), GFP_KERNEL);
>> +	if (!mm->counter)
>> +		return 0;
>> +	atomic_long_set(&mm->counter->usage, 0);
>> +	atomic_long_set(&mm->counter->limit, 0);
>> +	rwlock_init(&mm->container_lock);
>> +	return 1;
>> +}
> 
> ah-ha, we have another Documentation/SubmitChecklist customer.
> 
> It would be more conventional to make this return -EFOO on error,
> zero on success.
> 

ok.. I'll convert the functions to be consistent with the
"return 0 on success" philosophy.

>> +void memctlr_mm_free(struct mm_struct *mm)
>> +{
>> +	kfree(mm->counter);
>> +}
>> +
>> +static inline void memctlr_mm_assign_container_direct(struct mm_struct *mm,
>> +							struct container *cont)
>> +{
>> +	write_lock(&mm->container_lock);
>> +	mm->container = cont;
>> +	write_unlock(&mm->container_lock);
>> +}
> 
> More weird locking here.
> 

The container field of the mm_struct is protected by a read write spin lock.

>> +void memctlr_mm_assign_container(struct mm_struct *mm, struct task_struct *p)
>> +{
>> +	struct container *cont = task_container(p, &memctlr_subsys);
>> +	struct memctlr *mem = memctlr_from_cont(cont);
>> +
>> +	BUG_ON(!mem);
>> +	write_lock(&mm->container_lock);
>> +	mm->container = cont;
>> +	write_unlock(&mm->container_lock);
>> +}
> 
> And here.

Ditto.

> 
>> +/*
>> + * Update the rss usage counters for the mm_struct and the container it belongs
>> + * to. We do not fail rss for pages shared during fork (see copy_one_pte()).
>> + */
>> +int memctlr_update_rss(struct mm_struct *mm, int count, bool check)
>> +{
>> +	int ret = 1;
>> +	struct container *cont;
>> +	long usage, limit;
>> +	struct memctlr *mem;
>> +
>> +	read_lock(&mm->container_lock);
>> +	cont = mm->container;
>> +	read_unlock(&mm->container_lock);
>> +
>> +	if (!cont)
>> +		goto done;
> 
> And here.  I mean, if there was a reason for taking the lock around that
> read, then testing `cont' outside the lock just invalidated that reason.
> 

We took a consistent snapshot of cont. It cannot change outside the lock,
we check the value outside. I am sure I missed something.

>> +static inline void memctlr_double_lock(struct memctlr *mem1,
>> +					struct memctlr *mem2)
>> +{
>> +	if (mem1 > mem2) {
>> +		spin_lock(&mem1->lock);
>> +		spin_lock(&mem2->lock);
>> +	} else {
>> +		spin_lock(&mem2->lock);
>> +		spin_lock(&mem1->lock);
>> +	}
>> +}
> 
> Conventionally we take the lower-addressed lock first when doing this, not
> the higher-addressed one.
> 

Will fix this.

>> +static inline void memctlr_double_unlock(struct memctlr *mem1,
>> +						struct memctlr *mem2)
>> +{
>> +	if (mem1 > mem2) {
>> +		spin_unlock(&mem2->lock);
>> +		spin_unlock(&mem1->lock);
>> +	} else {
>> +		spin_unlock(&mem1->lock);
>> +		spin_unlock(&mem2->lock);
>> +	}
>> +}
>> +
>> ...
>>
>>  	retval = -ENOMEM;
>> +
>> +	if (!memctlr_update_rss(mm, 1, MEMCTLR_CHECK_LIMIT))
>> +		goto out;
>> +
> 
> Again, please use zero for success and -EFOO for error.
> 
> That way, you don't have to assume that the reason memctlr_update_rss()
> failed was out-of-memory.  Just propagate the error back.
> 

Yes, will do.

>>  	flush_dcache_page(page);
>>  	pte = get_locked_pte(mm, addr, &ptl);
>>  	if (!pte)
>> @@ -1580,6 +1587,9 @@ gotten:
>>  		cow_user_page(new_page, old_page, address, vma);
>>  	}
>>  
>> +	if (!memctlr_update_rss(mm, 1, MEMCTLR_CHECK_LIMIT))
>> +		goto oom;
>> +
>>  	/*
>>  	 * Re-check the pte - we dropped the lock
>>  	 */
>> @@ -1612,7 +1622,9 @@ gotten:
>>  		/* Free the old page.. */
>>  		new_page = old_page;
>>  		ret |= VM_FAULT_WRITE;
>> -	}
>> +	} else
>> +		memctlr_update_rss(mm, -1, MEMCTLR_DONT_CHECK_LIMIT);
> 
> This one doesn't get checked?
> 

Yes, because we are adding a -1, reducing the rss on failure.

> Why does MEMCTLR_DONT_CHECK_LIMIT exist?
> 

MEMCTLR_DONT_CHECK_LIMIT exists for the following reasons

1. Pages are shared during fork, fork() is not failed at that point
    since the pages are shared anyway, we allow the RSS limit to be
    exceeded.
2. When ZERO_PAGE is added, we don't check for limits (zeromap_pte_range).
3. On reducing RSS (passing -1 as the value)

-- 
	Warm Regards,
	Balbir Singh