Re: [PATCH] cpuset: mm: Reduce large amounts of memory barrier related damage v3
From: Mel Gorman <mgorman@suse.de>
Date: 2012-03-26 15:50:33
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lkml
On Mon, Mar 26, 2012 at 12:56:24PM +0200, Peter Zijlstra wrote:
quoted hunk ↗ jump to hunk
On Wed, 2012-03-07 at 18:08 +0000, Mel Gorman wrote:quoted
+ } while (!put_mems_allowed(cpuset_mems_cookie) && !page);Sorry for only noticing this now, but wouldn't it be better to first check page and only then bother with the put_mems_allowed() thing? That avoids the smp_rmb() and seqcount conditional all together in the likely case the allocation actually succeeded. <SNIP>diff --git a/mm/filemap.c b/mm/filemap.c index c3811bc..3b41553 100644 --- a/mm/filemap.c +++ b/mm/filemap.c@@ -504,7 +504,7 @@ struct page *__page_cache_alloc(gfp_t gfp) cpuset_mems_cookie = get_mems_allowed(); n = cpuset_mem_spread_node(); page = alloc_pages_exact_node(n, gfp, 0); - } while (!put_mems_allowed(cpuset_mems_cookie) && !page); + } while (!page && !put_mems_allowed(cpuset_mems_cookie)); return page; }
I think such a change would be better but should also rename the API. If developers see a get_foo type call, they will expect to see a put_foo call or assume it's a bug even though the implementation happens to be ok with that. Any suggestion on what a good new name would be? How about read_mems_allowed_begin() and read_mems_allowed_retry()? read_mems_allowed_begin would be a rename of get_mems_allowed(). In an error path, read_mems_allowed_retry() would documented to be *optionally* called when deciding whether to retry the operation or not. In this scheme, !put_mems_allowed would become read_mems_allowed_retry() which might be a bit easier to read overall. -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>