Re: [RFC] mm: Distinguish between mlocked and pinned pages
From: Andrew Morton <akpm@linux-foundation.org>
Date: 2011-08-17 22:54:19
Also in:
linux-rdma
On Wed, 10 Aug 2011 15:21:47 -0500 (CDT) Christoph Lameter [off-list ref] wrote:
Some kernel components pin user space memory (infiniband and perf) (by increasing the page count) and account that memory as "mlocked". The difference between mlocking and pinning is: A. mlocked pages are marked with PG_mlocked and are exempt from swapping. Page migration may move them around though. They are kept on a special LRU list. B. Pinned pages cannot be moved because something needs to directly access physical memory. They may not be on any LRU list. I recently saw an mlockalled process where mm->locked_vm became bigger than the virtual size of the process (!) because some memory was accounted for twice: Once when the page was mlocked and once when the Infiniband layer increased the refcount because it needt to pin the RDMA memory. This patch introduces a separate counter for pinned pages and accounts them seperately.
Sounds reasonable. But how do we prevent future confusion? We should carefully define these terms in an obvious place, please.
quoted hunk ↗ jump to hunk
--- linux-2.6.orig/include/linux/mm_types.h 2011-08-10 14:08:42.000000000 -0500 +++ linux-2.6/include/linux/mm_types.h 2011-08-10 14:09:02.000000000 -0500@@ -281,7 +281,7 @@ struct mm_struct { unsigned long hiwater_rss; /* High-watermark of RSS usage */ unsigned long hiwater_vm; /* High-water virtual memory usage */ - unsigned long total_vm, locked_vm, shared_vm, exec_vm; + unsigned long total_vm, locked_vm, pinned_vm, shared_vm, exec_vm; unsigned long stack_vm, reserved_vm, def_flags, nr_ptes; unsigned long start_code, end_code, start_data, end_data; unsigned long start_brk, brk, start_stack;
This is an obvious place. Could I ask that you split all these up into one-definition-per-line and we can start in on properly documenting each field? -- 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>