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From: Jayson R. King on 27 Feb 2010 02:30
From: Aneesh Kumar K.V <aneesh.kumar(a)linux.vnet.ibm.com>
Date: Thu Oct 16 10:09:17 2008 -0400
Subject: vfs: Add no_nrwrite_index_update writeback control flag

commit 17bc6c30cf6bfffd816bdc53682dd46fc34a2cf4 upstream.

If no_nrwrite_index_update is set we don't update nr_to_write and
address space writeback_index in write_cache_pages. This change
enables a file system to skip these updates in write_cache_pages and do
them in the writepages() callback. This patch will be followed by an
ext4 patch that make use of these new flags.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar(a)linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso(a)mit.edu>
CC: linux-fsdevel(a)vger.kernel.org
[dev(a)jaysonking.com: Modified the patch to account for subsequent changes in mainline being cherry-picked earlier for 2.6.27.y.]
Signed-off-by: Jayson R. King <dev(a)jaysonking.com>

---
include/linux/writeback.h | 9 +++++++++
mm/page-writeback.c | 14 +++++++++-----
2 files changed, 18 insertions(+), 5 deletions(-)

diff -urNp linux-2.6.27.orig/include/linux/writeback.h linux-2.6.27/include/linux/writeback.h
--- linux-2.6.27.orig/include/linux/writeback.h 2010-02-26 14:26:43.084252730 -0600
+++ linux-2.6.27/include/linux/writeback.h 2010-02-26 14:26:48.468252521 -0600
@@ -62,6 +62,15 @@ 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 */
+ /*
+ * write_cache_pages() won't update wbc->nr_to_write and
+ * mapping->writeback_index if no_nrwrite_index_update
+ * is set. write_cache_pages() may write more than we
+ * requested and we want to make sure nr_to_write and
+ * writeback_index are updated in a consistent manner
+ * so we use a single control to update them
+ */
+ unsigned no_nrwrite_index_update:1;
};

/*
diff -urNp linux-2.6.27.orig/mm/page-writeback.c linux-2.6.27/mm/page-writeback.c
--- linux-2.6.27.orig/mm/page-writeback.c 2010-02-26 14:26:43.085252646 -0600
+++ linux-2.6.27/mm/page-writeback.c 2010-02-26 14:26:48.469252852 -0600
@@ -878,6 +878,7 @@ int write_cache_pages(struct address_spa
pgoff_t done_index;
int cycled;
int range_whole = 0;
+ long nr_to_write = wbc->nr_to_write;

if (wbc->nonblocking && bdi_write_congested(bdi)) {
wbc->encountered_congestion = 1;
@@ -985,9 +986,9 @@ continue_unlock:
}
}

- if (wbc->nr_to_write > 0) {
- wbc->nr_to_write--;
- if (wbc->nr_to_write == 0 &&
+ if (nr_to_write > 0) {
+ nr_to_write--;
+ if (nr_to_write == 0 &&
wbc->sync_mode == WB_SYNC_NONE) {
/*
* We stop writing back only if we are
@@ -1024,8 +1025,11 @@ continue_unlock:
end = writeback_index - 1;
goto retry;
}
- if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
- mapping->writeback_index = done_index;
+ if (!wbc->no_nrwrite_index_update) {
+ if (wbc->range_cyclic || (range_whole && nr_to_write > 0))
+ mapping->writeback_index = done_index;
+ wbc->nr_to_write = nr_to_write;
+ }

return ret;
}
--
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Prev: [01/11] ext4: invalidate pages if delalloc block allocation fails.
Next: [02/11] percpu counter: clean up percpu_counter_sum_and_set()