Re: [RFC][PATCH] lru_add_drain_all() don't use schedule_on_each_cpu()

[Christoph Lameter <cl@linux-foundation.org>]

On Mon, 27 Oct 2008, Andrew Morton wrote:

> Can we fix that instead?

How about this fix?



Subject: Move migrate_prep out from under mmap_sem

Move the migrate_prep outside the mmap_sem for the following system calls

1. sys_move_pages
2. sys_migrate_pages
3. sys_mbind()

It really does not matter when we flush the lru. The system is free to add
pages onto the lru even during migration which will make the page 
migration either skip the page (mbind, migrate_pages) or return a busy 
state (move_pages).

Signed-off-by: Christoph Lameter <cl@linux-foundation.org>

Index: linux-2.6/mm/mempolicy.c
===================================================================
--- linux-2.6.orig/mm/mempolicy.c	2008-10-28 09:16:18.475514878 -0500
+++ linux-2.6/mm/mempolicy.c	2008-10-28 09:22:46.486773874 -0500
@@ -489,12 +489,6 @@
  	int err;
  	struct vm_area_struct *first, *vma, *prev;

-	if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) {
-
-		err = migrate_prep();
-		if (err)
-			return ERR_PTR(err);
-	}

  	first = find_vma(mm, start);
  	if (!first)
@@ -809,9 +803,13 @@
  	const nodemask_t *from_nodes, const nodemask_t *to_nodes, int flags)
  {
  	int busy = 0;
-	int err = 0;
+	int err;
  	nodemask_t tmp;

+	err = migrate_prep();
+	if (err)
+		return err;
+
  	down_read(&mm->mmap_sem);

  	err = migrate_vmas(mm, from_nodes, to_nodes, flags);
@@ -974,6 +972,12 @@
  		 start, start + len, mode, mode_flags,
  		 nmask ? nodes_addr(*nmask)[0] : -1);

+	if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) {
+
+		err = migrate_prep();
+		if (err)
+			return err;
+	}
  	down_write(&mm->mmap_sem);
  	vma = check_range(mm, start, end, nmask,
  			  flags | MPOL_MF_INVERT, &pagelist);
Index: linux-2.6/mm/migrate.c
===================================================================
--- linux-2.6.orig/mm/migrate.c	2008-10-28 09:15:46.578013464 -0500
+++ linux-2.6/mm/migrate.c	2008-10-28 09:16:14.038014180 -0500
@@ -841,12 +841,12 @@
  	struct page_to_node *pp;
  	LIST_HEAD(pagelist);

+	migrate_prep();
  	down_read(&mm->mmap_sem);

  	/*
  	 * Build a list of pages to migrate
  	 */
-	migrate_prep();
  	for (pp = pm; pp->node != MAX_NUMNODES; pp++) {
  		struct vm_area_struct *vma;
  		struct page *page;

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