Re: [PATCH 07/19] mm/mpol: Add MPOL_MF_NOOP
From: Andrea Arcangeli <hidden>
Date: 2012-08-09 21:44:20
On Tue, Jul 31, 2012 at 09:12:11PM +0200, Peter Zijlstra wrote:
From: Lee Schermerhorn <redacted> This patch augments the MPOL_MF_LAZY feature by adding a "NOOP" policy to mbind(). When the NOOP policy is used with the 'MOVE and 'LAZY flags, mbind() [check_range()] will walk the specified range and unmap eligible pages so that they will be migrated on next touch. This allows an application to prepare for a new phase of operation where different regions of shared storage will be assigned to worker threads, w/o changing policy. Note that we could just use "default" policy in this case. However, this also allows an application to request that pages be migrated, only if necessary, to follow any arbitrary policy that might currently apply to a range of pages, without knowing the policy, or without specifying multiple mbind()s for ranges with different policies.
This is a new kapi change. I could hardly understand the above so I wonder how long it will take before userland programmers will be familiar with MPOL_NOOP to actually use it in most apps? Could you just enable/disable your logics using a sysfs knob instead? enabling/disabling sched-numa is something an admin can easily do with a sysfs control, patching and rebuilding a proprietary app using mbind calls, no way, especially if the app is proprietary.
quoted hunk ↗ jump to hunk
Signed-off-by: Lee Schermerhorn <redacted> Cc: Rik van Riel <redacted> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Peter Zijlstra <redacted> --- include/linux/mempolicy.h | 1 + mm/mempolicy.c | 8 ++++---- 2 files changed, 5 insertions(+), 4 deletions(-)diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h index 87fabfa..668311a 100644 --- a/include/linux/mempolicy.h +++ b/include/linux/mempolicy.h@@ -21,6 +21,7 @@ enum { MPOL_BIND, MPOL_INTERLEAVE, MPOL_LOCAL, + MPOL_NOOP, /* retain existing policy for range */ MPOL_MAX, /* always last member of enum */ };diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 4fba5f2..251ef31 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c@@ -251,10 +251,10 @@ static struct mempolicy *mpol_new(unsigned short mode, unsigned short flags, pr_debug("setting mode %d flags %d nodes[0] %lx\n", mode, flags, nodes ? nodes_addr(*nodes)[0] : -1); - if (mode == MPOL_DEFAULT) { + if (mode == MPOL_DEFAULT || mode == MPOL_NOOP) { if (nodes && !nodes_empty(*nodes)) return ERR_PTR(-EINVAL); - return NULL; /* simply delete any existing policy */ + return NULL; } VM_BUG_ON(!nodes);@@ -1069,7 +1069,7 @@ static long do_mbind(unsigned long start, unsigned long len, if (start & ~PAGE_MASK) return -EINVAL; - if (mode == MPOL_DEFAULT) + if (mode == MPOL_DEFAULT || mode == MPOL_NOOP) flags &= ~MPOL_MF_STRICT; len = (len + PAGE_SIZE - 1) & PAGE_MASK;@@ -1121,7 +1121,7 @@ static long do_mbind(unsigned long start, unsigned long len, flags | MPOL_MF_INVERT, &pagelist); err = PTR_ERR(vma); /* maybe ... */ - if (!IS_ERR(vma)) + if (!IS_ERR(vma) && mode != MPOL_NOOP) err = mbind_range(mm, start, end, new); if (!err) {-- 1.7.2.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/