linux-kernel - Re: [RFC] Tracking mlocked pages and moving them off the LRU

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Message-ID: <Pine.LNX.4.64.0702051102150.20617@schroedinger.engr.sgi.com>
Date:	Mon, 5 Feb 2007 11:04:34 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Matt Mackall <mpm@...enic.com>
cc:	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Nick Piggin <nickpiggin@...oo.com.au>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [RFC] Tracking mlocked pages and moving them off the LRU

Patch seems to work and survives AIM7. However, we only know about 30% of 
the Mlocked pages after boot. With this additional patch to 
opportunistically move pages off the LRU immediately I can get the counter 
be accurate (for all practical purposes) like the non lazy version:


Index: current/mm/memory.c
===================================================================
--- current.orig/mm/memory.c	2007-02-05 10:44:10.000000000 -0800
+++ current/mm/memory.c	2007-02-05 11:01:46.000000000 -0800
@@ -919,6 +919,30 @@ void anon_add(struct vm_area_struct *vma
 }
 
 /*
+ * Opportunistically move the page off the LRU
+ * if possible. If we do not succeed then the LRU
+ * scans will take the page off.
+ */
+void try_to_set_mlocked(struct page *page)
+{
+	struct zone *zone;
+	unsigned long flags;
+
+	if (!PageLRU(page) || PageMlocked(page))
+		return;
+
+	zone = page_zone(page);
+	if (spin_trylock_irqsave(&zone->lru_lock, flags)) {
+		if (PageLRU(page) && !PageMlocked(page)) {
+			ClearPageLRU(page);
+			list_del(&page->lru);
+			SetPageMlocked(page);
+			__inc_zone_page_state(page, NR_MLOCK);
+		}
+		spin_unlock_irqrestore(&zone->lru_lock, flags);
+	}
+}
+/*
  * Do a quick page-table lookup for a single page.
  */
 struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
@@ -978,6 +1002,8 @@ struct page *follow_page(struct vm_area_
 			set_page_dirty(page);
 		mark_page_accessed(page);
 	}
+	if (vma->vm_flags & VM_LOCKED)
+		try_to_set_mlocked(page);
 unlock:
 	pte_unmap_unlock(ptep, ptl);
 out:
@@ -2271,6 +2297,8 @@ retry:
 		else {
 			inc_mm_counter(mm, file_rss);
 			page_add_file_rmap(new_page);
+			if (vma->vm_flags & VM_LOCKED)
+				try_to_set_mlocked(new_page);
 			if (write_access) {
 				dirty_page = new_page;
 				get_page(dirty_page);
-
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