On Fri, Oct 29, 2010 at 03:09:09PM +0800, Greg Thelen wrote:
> +
> + case MEMCG_NR_FILE_DIRTY:
> + /* Use Test{Set,Clear} to only un/charge the memcg once. */
> + if (val > 0) {
> + if (TestSetPageCgroupFileDirty(pc))
> + val = 0;
> + } else {
> + if (!TestClearPageCgroupFileDirty(pc))
> + val = 0;
> + }
I'm wondering why TestSet/TestClear and even the cgroup page flags for
dirty/writeback/unstable pages are necessary at all (it helps to
document in changelog if there are any). For example, VFS will call
TestSetPageDirty() before calling
mem_cgroup_inc_page_stat(MEMCG_NR_FILE_DIRTY), so there should be no
chance of false double counting.
Thanks,
Fengguang
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