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Date: Tue, 19 Oct 2010 21:18:20 +0530
From: Balbir Singh <balbir@...ux.vnet.ibm.com>
To: "Steven J. Magnani" <steve@...idescorp.com>
Cc: linux-mm@...ck.org, dhowells@...hat.com,
linux-kernel@...r.kernel.org, kamezawa.hiroyu@...fujitsu.com
Subject: Re: [PATCH V2] nommu: add anonymous page memcg accounting
* Steven J. Magnani <steve@...idescorp.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@...idescorp.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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