linux-ext4 - Re: [patch 4/8] mm: write_cache

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Date:	Fri, 10 Oct 2008 21:24:47 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Theodore Tso <tytso@....edu>,
	Steven Whitehouse <steve@...gwyn.com>, npiggin@...e.de,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mikulas Patocka <mpatocka@...hat.com>, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [patch 4/8] mm: write_cache_pages type overflow fix

On Fri, Oct 10, 2008 at 10:08:29AM -0400, Christoph Hellwig wrote:
> On Fri, Oct 10, 2008 at 10:05:35AM -0400, Theodore Tso wrote:
> > 3) A version which (optionally via a flag in the wbc structure)
> > instructs write_cache_pages() to not pursue those updates.  This has
> > not been written yet.
> 
> This one sounds best to me (although we'd have to actualy see it..)

something like  the below ?

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index bd91987..7599af2 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -63,6 +63,8 @@ struct writeback_control {
 	unsigned for_writepages:1;	/* This is a writepages() call */
 	unsigned range_cyclic:1;	/* range_start is cyclic */
 	unsigned more_io:1;		/* more io to be dispatched */
+	/* flags which control the write_cache_pages behaviour */
+	int writeback_flags;
 };
 
 /*
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 718efa6..c198ead 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -876,11 +876,18 @@ int write_cache_pages(struct address_space *mapping,
 	pgoff_t end;		/* Inclusive */
 	int scanned = 0;
 	int range_whole = 0;
+	int flags = wbc->writeback_flags;
+	long *nr_to_write, count;
 
 	if (wbc->nonblocking && bdi_write_congested(bdi)) {
 		wbc->encountered_congestion = 1;
 		return 0;
 	}
+	if (flags & WB_NO_NRWRITE_UPDATE) {
+		count  = wbc->nr_to_write;
+		nr_to_write = &count;
+	} else
+		nr_to_write = &wbc->nr_to_write;
 
 	pagevec_init(&pvec, 0);
 	if (wbc->range_cyclic) {
@@ -939,7 +946,7 @@ int write_cache_pages(struct address_space *mapping,
 				unlock_page(page);
 				ret = 0;
 			}
-			if (ret || (--(wbc->nr_to_write) <= 0))
+			if (ret || (--(*nr_to_write) <= 0))
 				done = 1;
 			if (wbc->nonblocking && bdi_write_congested(bdi)) {
 				wbc->encountered_congestion = 1;
@@ -958,8 +965,11 @@ int write_cache_pages(struct address_space *mapping,
 		index = 0;
 		goto retry;
 	}
-	if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
+	if ((wbc->range_cyclic ||
+			(range_whole && wbc->nr_to_write > 0)) && 
+			(flags & ~WB_NO_INDEX_UPDATE)) {
 		mapping->writeback_index = index;
+	}
 
 	return ret;
 }
--
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