[PATCH] Fix ext2 and ext4 buffer-head accounting.

[PATCH] Fix ext2 and ext4 buffer-head accounting.

[Ying Han]

Pages pinned to block group_descriptors in the super_block are non-reclaimable.
Those pages are showed up as file-backed in meminfo which confuse user program
issuing too many drop_caches/ttfp when this memory will never be freed.

The change has us not account for the file system descriptors by taking the pages
off LRU and decrementing the NR_FILE_PAGES counter. The pages are putting back when
the filesystem is being unmounted.

Signed-off-by: Ying Han <yinghan@google.com>
Signed-off-by: Paul Turner <pjt@google.com>
---
 fs/buffer.c                 |   44 +++++++++++++++++++++++++++++++++++++++++++
 fs/ext2/super.c             |   15 +++++++++++++-
 fs/ext4/super.c             |   12 ++++++++++-
 include/linux/buffer_head.h |    5 ++++
 4 files changed, 74 insertions(+), 2 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 3e7dca2..677d5f1 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -22,6 +22,8 @@
 #include <linux/syscalls.h>
 #include <linux/fs.h>
 #include <linux/mm.h>
+#include <linux/memcontrol.h>
+#include <linux/mm_inline.h>
 #include <linux/percpu.h>
 #include <linux/slab.h>
 #include <linux/capability.h>
@@ -3314,6 +3316,48 @@ int bh_submit_read(struct buffer_head *bh)
 }
 EXPORT_SYMBOL(bh_submit_read);
 
+void bh_disable_accounting(struct buffer_head *bh)
+{
+	struct page *page = bh->b_page;
+	struct zone *zone = page_zone(page);
+	unsigned long flags;
+
+	if (buffer_unaccounted(bh))
+		return;
+
+	spin_lock_irqsave(&zone->lru_lock, flags);
+	/* If someone else is holding it off-LRU we can't safely do anything */
+	if (PageLRU(page)) {
+		BUG_ON(buffer_unaccounted(bh));
+		ClearPageLRU(page);
+		del_page_from_lru(zone, page);
+		__dec_zone_state(zone, NR_FILE_PAGES);
+		set_buffer_unaccounted(bh);
+	}
+	spin_unlock_irqrestore(&zone->lru_lock, flags);
+}
+EXPORT_SYMBOL(bh_disable_accounting);
+
+void bh_enable_accounting(struct buffer_head *bh)
+{
+	struct page *page = bh->b_page;
+	struct zone *zone = page_zone(page);
+	unsigned long flags;
+
+	if (!buffer_unaccounted(bh))
+		return;
+
+	spin_lock_irqsave(&zone->lru_lock, flags);
+	if (buffer_unaccounted(bh)) {
+		SetPageLRU(page);
+		add_page_to_lru_list(zone, page, LRU_INACTIVE_FILE);
+		__inc_zone_state(zone, NR_FILE_PAGES);
+		clear_buffer_unaccounted(bh);
+	}
+	spin_unlock_irqrestore(&zone->lru_lock, flags);
+}
+EXPORT_SYMBOL(bh_enable_accounting);
+
 void __init buffer_init(void)
 {
 	int nrpages;
diff --git a/fs/ext2/super.c b/fs/ext2/super.c
index 1ec6026..a4d21ce 100644
--- a/fs/ext2/super.c
+++ b/fs/ext2/super.c
@@ -29,6 +29,7 @@
 #include <linux/vfs.h>
 #include <linux/seq_file.h>
 #include <linux/mount.h>
+#include <linux/swap.h>
 #include <linux/log2.h>
 #include <linux/quotaops.h>
 #include <asm/uaccess.h>
@@ -135,13 +136,16 @@ static void ext2_put_super (struct super_block * sb)
 	}
 	db_count = sbi->s_gdb_count;
 	for (i = 0; i < db_count; i++)
-		if (sbi->s_group_desc[i])
+		if (sbi->s_group_desc[i]) {
+			bh_enable_accounting(sbi->s_group_desc[i]);
 			brelse (sbi->s_group_desc[i]);
+		}
 	kfree(sbi->s_group_desc);
 	kfree(sbi->s_debts);
 	percpu_counter_destroy(&sbi->s_freeblocks_counter);
 	percpu_counter_destroy(&sbi->s_freeinodes_counter);
 	percpu_counter_destroy(&sbi->s_dirs_counter);
+	bh_enable_accounting(sbi->s_sbh);
 	brelse (sbi->s_sbh);
 	sb->s_fs_info = NULL;
 	kfree(sbi->s_blockgroup_lock);
@@ -1080,9 +1084,18 @@ static int ext2_fill_super(struct super_block *sb, void *data, int silent)
 	if (EXT2_HAS_COMPAT_FEATURE(sb, EXT3_FEATURE_COMPAT_HAS_JOURNAL))
 		ext2_msg(sb, KERN_WARNING,
 			"warning: mounting ext3 filesystem as ext2");
+
 	if (ext2_setup_super (sb, es, sb->s_flags & MS_RDONLY))
 		sb->s_flags |= MS_RDONLY;
 	ext2_write_super(sb);
+
+	/* disable accounting of pinned file pages */
+	lru_add_drain_all();
+	db_count = sbi->s_gdb_count;
+	for (i = 0; i < db_count; i++)
+		bh_disable_accounting(sbi->s_group_desc[i]);
+	bh_disable_accounting(sbi->s_sbh);
+
 	return 0;
 
 cantfind_ext2:
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 2614774..5203476 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -32,6 +32,7 @@
 #include <linux/vfs.h>
 #include <linux/random.h>
 #include <linux/mount.h>
+#include <linux/swap.h>
 #include <linux/namei.h>
 #include <linux/quotaops.h>
 #include <linux/seq_file.h>
@@ -734,8 +735,10 @@ static void ext4_put_super(struct super_block *sb)
 	}
 	kobject_del(&sbi->s_kobj);
 
-	for (i = 0; i < sbi->s_gdb_count; i++)
+	for (i = 0; i < sbi->s_gdb_count; i++) {
+		bh_enable_accounting(sbi->s_group_desc[i]);
 		brelse(sbi->s_group_desc[i]);
+	}
 	kfree(sbi->s_group_desc);
 	if (is_vmalloc_addr(sbi->s_flex_groups))
 		vfree(sbi->s_flex_groups);
@@ -745,6 +748,7 @@ static void ext4_put_super(struct super_block *sb)
 	percpu_counter_destroy(&sbi->s_freeinodes_counter);
 	percpu_counter_destroy(&sbi->s_dirs_counter);
 	percpu_counter_destroy(&sbi->s_dirtyblocks_counter);
+	bh_enable_accounting(sbi->s_sbh);
 	brelse(sbi->s_sbh);
 #ifdef CONFIG_QUOTA
 	for (i = 0; i < MAXQUOTAS; i++)
@@ -3129,6 +3133,12 @@ no_journal:
 		goto failed_mount4;
 	}
 
+	/* disable accounting of pinned file pages */
+	lru_add_drain_all();
+	for (i = 0; i < db_count; i++)
+		bh_disable_accounting(sbi->s_group_desc[i]);
+	bh_disable_accounting(sbi->s_sbh);
+
 	sbi->s_kobj.kset = ext4_kset;
 	init_completion(&sbi->s_kobj_unregister);
 	err = kobject_init_and_add(&sbi->s_kobj, &ext4_ktype, NULL,
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index ec94c12..7d48499 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -34,6 +34,7 @@ enum bh_state_bits {
 	BH_Write_EIO,	/* I/O error on write */
 	BH_Eopnotsupp,	/* operation not supported (barrier) */
 	BH_Unwritten,	/* Buffer is allocated on disk but not written */
+	BH_Unaccounted, /* Backing page has been removed from accounting */
 	BH_Quiet,	/* Buffer Error Prinks to be quiet */
 
 	BH_PrivateStart,/* not a state bit, but the first bit available
@@ -126,6 +127,7 @@ BUFFER_FNS(Boundary, boundary)
 BUFFER_FNS(Write_EIO, write_io_error)
 BUFFER_FNS(Eopnotsupp, eopnotsupp)
 BUFFER_FNS(Unwritten, unwritten)
+BUFFER_FNS(Unaccounted, unaccounted)
 
 #define bh_offset(bh)		((unsigned long)(bh)->b_data & ~PAGE_MASK)
 #define touch_buffer(bh)	mark_page_accessed(bh->b_page)
@@ -234,6 +236,9 @@ int nobh_truncate_page(struct address_space *, loff_t, get_block_t *);
 int nobh_writepage(struct page *page, get_block_t *get_block,
                         struct writeback_control *wbc);
 
+void bh_disable_accounting(struct buffer_head *bh);
+void bh_enable_accounting(struct buffer_head *bh);
+
 void buffer_init(void);
 
 /*
-- 
1.7.1

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Re: [PATCH] Fix ext2 and ext4 buffer-head accounting.

[Andrew Morton]

On Wed, 27 Oct 2010 10:16:37 -0700
Ying Han <yinghan@google.com> wrote:

> Pages pinned to block group_descriptors in the super_block are non-reclaimable.
> Those pages are showed up as file-backed in meminfo which confuse user program
> issuing too many drop_caches/ttfp when this memory will never be freed.
> 
> The change has us not account for the file system descriptors by taking the pages
> off LRU and decrementing the NR_FILE_PAGES counter. The pages are putting back when
> the filesystem is being unmounted.

Well, it's not just ext2 and ext4.

Is this the simplest way of solving the problem?  This is just pinned
pagecache.  We already have way of handling pinned pagecache (eg,
mlocked pages).  Can we reuse those mechanisms, perhaps after suitable
generalisation?



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