Re: [PATCH V2] nommu: add anonymous page memcg accounting

[Balbir Singh <balbir@linux.vnet.ibm.com>]

* Steven J. Magnani <steve@digidescorp.com> [2010-10-19 07:34:14]:

> Add the necessary calls to track VM anonymous page usage (only).
> 
> V2 changes:
> * Added update of memory cgroup documentation
> * Clarify use of 'file' to distinguish anonymous mappings
> 
> Signed-off-by: Steven J. Magnani <steve@digidescorp.com>
> ---
> diff -uprN a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
> --- a/Documentation/cgroups/memory.txt	2010-10-05 09:14:36.000000000 -0500
> +++ b/Documentation/cgroups/memory.txt	2010-10-19 07:28:04.000000000 -0500
> @@ -34,6 +34,7 @@ Current Status: linux-2.6.34-mmotm(devel
> 
>  Features:
>   - accounting anonymous pages, file caches, swap caches usage and limiting them.
> +   NOTE: On NOMMU systems, only anonymous pages are accounted.
>   - private LRU and reclaim routine. (system's global LRU and private LRU
>     work independently from each other)
>   - optionally, memory+swap usage can be accounted and limited.
> @@ -640,7 +641,30 @@ At reading, current status of OOM is sho
>  	under_oom	 0 or 1 (if 1, the memory cgroup is under OOM, tasks may
>  				 be stopped.)
> 
> -11. TODO
> +11. NOMMU Support
> +
> +Systems without a Memory Management Unit do not support virtual memory,
> +swapping, page faults, or migration, and are therefore limited to operating
> +entirely within the system's RAM. On such systems, maintaining an ability to
> +allocate sufficiently large blocks of contiguous memory is usually a challenge.
> +This makes the overhead involved in memory cgroup support more of a concern,
> +particularly when the memory page size is small.
> +
> +Typically, embedded systems are comparatively simple and deterministic, and are
> +required to remain stable over long periods. Invocation of the OOM-killer, were
> +it to occur in an uncontrolled manner, would likely destabilize such systems.
> +
> +Even a well-designed system may be presented with external stimuli that could
> +lead to OOM conditions. One example is a system that is required to check a
> +user-supplied removable FAT filesystem. As there is no way to bound the size
> +or coherence of the user's filesystem, the memory required to run dosfsck on
> +it may exceed the system's capacity. Running dosfsck in a memory cgroup
> +can preserve system stability even in the face of excessive memory demands.
> +
> +At the present time, only anonymous pages are included in NOMMU memory cgroup
> +accounting.

What is the reason for tracking just anonymous memory?

> +
> +12. TODO
> 
>  1. Add support for accounting huge pages (as a separate controller)
>  2. Make per-cgroup scanner reclaim not-shared pages first
> diff -uprN a/mm/nommu.c b/mm/nommu.c
> --- a/mm/nommu.c	2010-10-13 08:20:38.000000000 -0500
> +++ b/mm/nommu.c	2010-10-13 08:24:06.000000000 -0500
> @@ -524,8 +524,10 @@ static void delete_nommu_region(struct v
>  /*
>   * free a contiguous series of pages
>   */
> -static void free_page_series(unsigned long from, unsigned long to)
> +static void free_page_series(unsigned long from, unsigned long to,
> +			     const struct file *file)
>  {
> +	mem_cgroup_uncharge_start();
>  	for (; from < to; from += PAGE_SIZE) {
>  		struct page *page = virt_to_page(from);
> 
> @@ -534,8 +536,13 @@ static void free_page_series(unsigned lo
>  		if (page_count(page) != 1)
>  			kdebug("free page %p: refcount not one: %d",
>  			       page, page_count(page));
> +		/* Only anonymous pages are charged, currently */
> +		if (!file)
> +			mem_cgroup_uncharge_page(page);
> +
>  		put_page(page);
>  	}
> +	mem_cgroup_uncharge_end();
>  }
> 
>  /*
> @@ -563,7 +570,8 @@ static void __put_nommu_region(struct vm
>  		 * from ramfs/tmpfs mustn't be released here */
>  		if (region->vm_flags & VM_MAPPED_COPY) {
>  			kdebug("free series");
> -			free_page_series(region->vm_start, region->vm_top);
> +			free_page_series(region->vm_start, region->vm_top,
> +					 region->vm_file);
>  		}
>  		kmem_cache_free(vm_region_jar, region);
>  	} else {
> @@ -1117,9 +1125,27 @@ static int do_mmap_private(struct vm_are
>  		set_page_refcounted(&pages[point]);
> 
>  	base = page_address(pages);
> -	region->vm_flags = vma->vm_flags |= VM_MAPPED_COPY;
> +
>  	region->vm_start = (unsigned long) base;
>  	region->vm_end   = region->vm_start + rlen;
> +
> +	/* Only anonymous pages are charged, currently */
> +	if (!vma->vm_file) {
> +		for (point = 0; point < total; point++) {
> +			int charge_failed =
> +				mem_cgroup_newpage_charge(&pages[point],
> +							  current->mm,

Is current->mm same as vma->vm_mm? I think vma->vm_mm is cleaner.

> +							  GFP_KERNEL);
> +			if (charge_failed) {
> +				free_page_series(region->vm_start,
> +						 region->vm_end, NULL);
> +				region->vm_start = region->vm_end = 0;
> +				goto enomem;
> +			}
> +		}
> +	}
> +
> +	region->vm_flags = vma->vm_flags |= VM_MAPPED_COPY;
>  	region->vm_top   = region->vm_start + (total << PAGE_SHIFT);
> 
>  	vma->vm_start = region->vm_start;
> @@ -1150,7 +1176,7 @@ static int do_mmap_private(struct vm_are
>  	return 0;
> 
>  error_free:
> -	free_page_series(region->vm_start, region->vm_end);
> +	free_page_series(region->vm_start, region->vm_end, vma->vm_file);
>  	region->vm_start = vma->vm_start = 0;
>  	region->vm_end   = vma->vm_end = 0;
>  	region->vm_top   = 0;
> @@ -1555,7 +1581,7 @@ static int shrink_vma(struct mm_struct *
>  	add_nommu_region(region);
>  	up_write(&nommu_region_sem);
> 
> -	free_page_series(from, to);
> +	free_page_series(from, to, vma->vm_file);
>  	return 0;
>  }
> 
> 
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-- 
	Three Cheers,
	Balbir

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