linux-kernel - Re: [PATCH 11/15] writeback: skip balance_dirty

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Date:	Sat, 11 Jun 2011 21:07:31 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Jan Kara <jack@...e.cz>, Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Dave Chinner <david@...morbit.com>,
	Christoph Hellwig <hch@...radead.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 11/15] writeback: skip balance_dirty_pages() for
 in-memory fs

> @@ -495,6 +490,9 @@ static void balance_dirty_pages(struct a
>  	bool dirty_exceeded = false;
>  	struct backing_dev_info *bdi = mapping->backing_dev_info;
>  
> +	if (!bdi_cap_account_dirty(bdi))
> +		return;
> +
>  	for (;;) {
>  		struct writeback_control wbc = {
>  			.sync_mode	= WB_SYNC_NONE,
> 

Update: it's slightly better to do early return in
balance_dirty_pages_ratelimited_nr(). This way the tmpfs dirties won't
unnecessarily disturb the per-cpu bdp_ratelimits counters.

Thanks,
Fengguang
---

--- linux-next.orig/mm/page-writeback.c	2011-06-11 17:52:59.000000000 +0800
+++ linux-next/mm/page-writeback.c	2011-06-11 17:53:53.000000000 +0800
@@ -1098,9 +1098,6 @@ static void balance_dirty_pages(struct a
 	struct backing_dev_info *bdi = mapping->backing_dev_info;
 	unsigned long start_time = jiffies;
 
-	if (!bdi_cap_account_dirty(bdi))
-		return;
-
 	for (;;) {
 		nr_reclaimable = global_page_state(NR_FILE_DIRTY) +
 					global_page_state(NR_UNSTABLE_NFS);
@@ -1237,9 +1234,13 @@ static DEFINE_PER_CPU(unsigned long, bdp
 void balance_dirty_pages_ratelimited_nr(struct address_space *mapping,
 					unsigned long nr_pages_dirtied)
 {
+	struct backing_dev_info *bdi = mapping->backing_dev_info;
 	unsigned long ratelimit;
 	unsigned long *p;
 
+	if (!bdi_cap_account_dirty(bdi))
+		return;
+
 	ratelimit = ratelimit_pages;
 	if (mapping->backing_dev_info->dirty_exceeded)
 		ratelimit = 8;
--
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