[PATCH v3 1/4] btrfs: refactor @nrptrs calculation of btrfs_buffered_write()

Qu Wenruo
2020-08-25T05:48:27Z

@nrptrs of btrfs_bufferd_write() determines the up limit of pages we can
process in one batch.

Refactor that calculation into its own function, and fix a small page
alignment bug where the result can be one page less than ideal.

Despite that, no functionality change.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
fs/btrfs/file.c | 24 ++++++++++++++++++++----
1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 5a818ebcb01f..64f744989697 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1620,6 +1620,25 @@ void btrfs_check_nocow_unlock(struct btrfs_inode *inode)
btrfs_drew_write_unlock(&inode->root->snapshot_lock);
}

+/* Helper to get how many pages we should alloc for the batch */
+static int calc_nr_pages(loff_t pos, struct iov_iter *iov)
+{
+ int nr_pages;
+
+ /*
+ * Try to cover the full iov range, as btrfs metadata/data reserve
+ * and release can be pretty slow, thus the more pages we process in
+ * one batch the better.
+ */
+ nr_pages = (round_up(pos + iov_iter_count(iov), PAGE_SIZE) -
+ round_down(pos, PAGE_SIZE)) / PAGE_SIZE;
+
+ nr_pages = min(nr_pages, current->nr_dirtied_pause -
+ current->nr_dirtied);
+ nr_pages = max(nr_pages, 8);
+ return nr_pages;
+}
+
static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb,
struct iov_iter *i)
{
@@ -1638,10 +1657,7 @@ static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb,
bool only_release_metadata = false;
bool force_page_uptodate = false;

- nrptrs = min(DIV_ROUND_UP(iov_iter_count(i), PAGE_SIZE),
- PAGE_SIZE / (sizeof(struct page *)));
- nrptrs = min(nrptrs, current->nr_dirtied_pause - current->nr_dirtied);
- nrptrs = max(nrptrs, 8);
+ nrptrs = calc_nr_pages(pos, i);
pages = kmalloc_array(nrptrs, sizeof(struct page *), GFP_KERNEL);
if (!pages)
return -ENOMEM;
--
2.28.0