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Message-ID: <20130719165037.GA18358@tucsk.piliscsaba.szeredi.hu>
Date: Fri, 19 Jul 2013 18:50:37 +0200
From: Miklos Szeredi <miklos@...redi.hu>
To: Maxim Patlasov <MPatlasov@...allels.com>
Cc: riel@...hat.com, dev@...allels.com, xemul@...allels.com,
fuse-devel@...ts.sourceforge.net, bfoster@...hat.com,
linux-kernel@...r.kernel.org, jbottomley@...allels.com,
linux-mm@...ck.org, viro@...iv.linux.org.uk,
linux-fsdevel@...r.kernel.org, akpm@...ux-foundation.org,
fengguang.wu@...el.com, devel@...nvz.org, mgorman@...e.de
Subject: Re: [PATCH 10/16] fuse: Implement writepages callback
On Sat, Jun 29, 2013 at 09:45:29PM +0400, Maxim Patlasov wrote:
> From: Pavel Emelyanov <xemul@...nvz.org>
>
> The .writepages one is required to make each writeback request carry more than
> one page on it. The patch enables optimized behaviour unconditionally,
> i.e. mmap-ed writes will benefit from the patch even if fc->writeback_cache=0.
I rewrote this a bit, so we won't have to do the thing in two passes, which
makes it simpler and more robust. Waiting for page writeback here is wrong
anyway, see comment above fuse_page_mkwrite(). BTW we had a race there because
fuse_page_mkwrite() didn't take the page lock. I've also fixed that up and
pushed a series containing these patches up to implementing ->writepages() to
git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse.git writepages
Passed some trivial testing but more is needed.
I'll get to the rest of the patches next week.
Thanks,
Miklos
Subject: fuse: Implement writepages callback
From: Pavel Emelyanov <xemul@...nvz.org>
Date: Sat, 29 Jun 2013 21:45:29 +0400
The .writepages one is required to make each writeback request carry more than
one page on it. The patch enables optimized behaviour unconditionally,
i.e. mmap-ed writes will benefit from the patch even if fc->writeback_cache=0.
[SzM: simplify, add comments]
Signed-off-by: Maxim Patlasov <MPatlasov@...allels.com>
Signed-off-by: Miklos Szeredi <mszeredi@...e.cz>
---
fs/fuse/file.c | 139 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 139 insertions(+)
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1579,6 +1579,144 @@ static int fuse_writepage(struct page *p
return err;
}
+struct fuse_fill_wb_data {
+ struct fuse_req *req;
+ struct fuse_file *ff;
+ struct inode *inode;
+};
+
+static void fuse_writepages_send(struct fuse_fill_wb_data *data)
+{
+ struct fuse_req *req = data->req;
+ struct inode *inode = data->inode;
+ struct fuse_conn *fc = get_fuse_conn(inode);
+ struct fuse_inode *fi = get_fuse_inode(inode);
+
+ req->ff = fuse_file_get(data->ff);
+ spin_lock(&fc->lock);
+ list_add_tail(&req->list, &fi->queued_writes);
+ fuse_flush_writepages(inode);
+ spin_unlock(&fc->lock);
+}
+
+static int fuse_writepages_fill(struct page *page,
+ struct writeback_control *wbc, void *_data)
+{
+ struct fuse_fill_wb_data *data = _data;
+ struct fuse_req *req = data->req;
+ struct inode *inode = data->inode;
+ struct fuse_conn *fc = get_fuse_conn(inode);
+ struct page *tmp_page;
+ int err;
+
+ if (req) {
+ BUG_ON(!req->num_pages);
+ if (req->num_pages == FUSE_MAX_PAGES_PER_REQ ||
+ (req->num_pages + 1) * PAGE_CACHE_SIZE > fc->max_write ||
+ req->pages[req->num_pages - 1]->index + 1 != page->index) {
+
+ fuse_writepages_send(data);
+ data->req = NULL;
+ }
+ }
+ err = -ENOMEM;
+ tmp_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
+ if (!tmp_page)
+ goto out_unlock;
+
+ /*
+ * The page must not be redirtied until the writeout is completed
+ * (i.e. userspace has sent a reply to the write request). Otherwise
+ * there could be more than one temporary page instance for each real
+ * page.
+ *
+ * This is ensured by holding the page lock in page_mkwrite() while
+ * checking fuse_page_is_writeback(). We already hold the page lock
+ * since clear_page_dirty_for_io() and keep it held until we add the
+ * request to the fi->writepages list and increment req->num_pages.
+ * After this fuse_page_is_writeback() will indicate that the page is
+ * under writeback, so we can release the page lock.
+ */
+ if (data->req == NULL) {
+ struct fuse_inode *fi = get_fuse_inode(inode);
+
+ err = -ENOMEM;
+ req = fuse_request_alloc_nofs(FUSE_MAX_PAGES_PER_REQ);
+ if (!req) {
+ __free_page(tmp_page);
+ goto out_unlock;
+ }
+
+ fuse_write_fill(req, data->ff, page_offset(page), 0);
+ req->misc.write.in.write_flags |= FUSE_WRITE_CACHE;
+ req->in.argpages = 1;
+ req->background = 1;
+ req->num_pages = 0;
+ req->end = fuse_writepage_end;
+ req->inode = inode;
+
+ spin_lock(&fc->lock);
+ list_add(&req->writepages_entry, &fi->writepages);
+ spin_unlock(&fc->lock);
+
+ data->req = req;
+ }
+ set_page_writeback(page);
+
+ copy_highpage(tmp_page, page);
+ req->pages[req->num_pages] = tmp_page;
+ req->page_descs[req->num_pages].offset = 0;
+ req->page_descs[req->num_pages].length = PAGE_SIZE;
+
+ inc_bdi_stat(page->mapping->backing_dev_info, BDI_WRITEBACK);
+ inc_zone_page_state(tmp_page, NR_WRITEBACK_TEMP);
+ end_page_writeback(page);
+
+ /*
+ * Protected by fc->lock against concurrent access by
+ * fuse_page_is_writeback().
+ */
+ spin_lock(&fc->lock);
+ req->num_pages++;
+ spin_unlock(&fc->lock);
+
+ err = 0;
+out_unlock:
+ unlock_page(page);
+
+ return err;
+}
+
+static int fuse_writepages(struct address_space *mapping,
+ struct writeback_control *wbc)
+{
+ struct inode *inode = mapping->host;
+ struct fuse_conn *fc = get_fuse_conn(inode);
+ struct fuse_fill_wb_data data;
+ int err;
+
+ err = -EIO;
+ if (is_bad_inode(inode))
+ goto out;
+
+ data.req = NULL;
+ data.inode = inode;
+ data.ff = fuse_write_file(fc, get_fuse_inode(inode));
+ if (!data.ff)
+ goto out;
+
+ err = write_cache_pages(mapping, wbc, fuse_writepages_fill, &data);
+ if (data.req) {
+ /* Ignore errors if we can write at least one page */
+ BUG_ON(!data.req->num_pages);
+ fuse_writepages_send(&data);
+ err = 0;
+ }
+ fuse_file_put(data.ff, false);
+out:
+ return err;
+}
+
static int fuse_launder_page(struct page *page)
{
int err = 0;
@@ -2589,6 +2727,7 @@ static const struct file_operations fuse
static const struct address_space_operations fuse_file_aops = {
.readpage = fuse_readpage,
.writepage = fuse_writepage,
+ .writepages = fuse_writepages,
.launder_page = fuse_launder_page,
.readpages = fuse_readpages,
.set_page_dirty = __set_page_dirty_nobuffers,
--
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