Hi Christoph,
On Mon, Sep 02, 2019 at 11:58:03PM -0700, Christoph Hellwig wrote:
> On Mon, Sep 02, 2019 at 11:50:38PM +0800, Gao Xiang wrote:
> > > > You means killing erofs_get_meta_page or avoid erofs_read_raw_page?
> > > >
> > > > - For killing erofs_get_meta_page, here is the current erofs_get_meta_page:
> > >
> > > > I think it is simple enough. read_cache_page need write a similar
> > > > filler, or read_cache_page_gfp will call .readpage, and then
> > > > introduce buffer_heads, that is what I'd like to avoid now (no need these
> > > > bd_inode buffer_heads in memory...)
> > >
> > > If using read_cache_page_gfp and ->readpage works, please do. The
> > > fact that the block device inode uses buffer heads is an implementation
> > > detail that might not last very long and should be invisible to you.
> > > It also means you can get rid of a lot of code that you don't have
> > > to maintain and others don't have to update for global API changes.
> >
> > I care about those useless buffer_heads in memory for our products...
> >
> > Since we are nobh filesystem (a little request, could I use it
> > after buffer_heads are fully avoided, I have no idea why I need
> > those buffer_heads in memory.... But I think bd_inode is good
> > for caching metadata...)
>
> Then please use read_cache_page with iomap_readpage(s), and write
> comment explaining why your are not using read_cache_page_gfp.
I implement a prelimitary version, but I have no idea it is a really
cleanup for now.
>From 001e3e64c81e4ced0d22b147e6abf90060e704b5 Mon Sep 17 00:00:00 2001
From: Gao Xiang <gaoxiang25@xxxxxxxxxx>
Date: Tue, 3 Sep 2019 16:13:00 +0800
Subject: [PATCH] erofs: use iomap_readpage for erofs_get_meta_page
Signed-off-by: Gao Xiang <gaoxiang25@xxxxxxxxxx>
---
fs/erofs/Kconfig | 1 +
fs/erofs/data.c | 91 ++++++++++++++++++++++++++----------------------
2 files changed, 51 insertions(+), 41 deletions(-)
diff --git a/fs/erofs/Kconfig b/fs/erofs/Kconfig
index 9d634d3a1845..c9eeb0bf4737 100644
--- a/fs/erofs/Kconfig
+++ b/fs/erofs/Kconfig
@@ -3,6 +3,7 @@
config EROFS_FS
tristate "EROFS filesystem support"
depends on BLOCK
+ select FS_IOMAP
help
EROFS (Enhanced Read-Only File System) is a lightweight
read-only file system with modern designs (eg. page-sized
diff --git a/fs/erofs/data.c b/fs/erofs/data.c
index 3881c0689134..34c6e05fab71 100644
--- a/fs/erofs/data.c
+++ b/fs/erofs/data.c
@@ -5,6 +5,9 @@
* Created by Gao Xiang <gaoxiang25@xxxxxxxxxx>
*/
#include "internal.h"
+#include <linux/iomap.h>
+#include <linux/mpage.h>
+#include <linux/sched/mm.h>
#include <linux/prefetch.h>
#include <trace/events/erofs.h>
@@ -51,54 +54,60 @@ static struct bio *erofs_grab_raw_bio(struct super_block *sb,
return bio;
}
-struct page *erofs_get_meta_page(struct super_block *sb, erofs_blk_t blkaddr)
+static int erofs_meta_iomap_begin(struct inode *inode, loff_t pos,
+ loff_t length, unsigned int flags,
+ struct iomap *iomap)
{
- struct inode *const bd_inode = sb->s_bdev->bd_inode;
- struct address_space *const mapping = bd_inode->i_mapping;
- /* prefer retrying in the allocator to blindly looping below */
- const gfp_t gfp = mapping_gfp_constraint(mapping, ~__GFP_FS);
- struct page *page;
- int err;
-
-repeat:
- page = find_or_create_page(mapping, blkaddr, gfp);
- if (!page)
- return ERR_PTR(-ENOMEM);
-
- DBG_BUGON(!PageLocked(page));
-
- if (!PageUptodate(page)) {
- struct bio *bio;
+ const unsigned int blkbits = inode->i_blkbits;
+
+ iomap->flags = 0;
+ iomap->bdev = I_BDEV(inode);
+ iomap->offset = round_down(pos, 1 << blkbits);
+ iomap->addr = iomap->offset;
+ iomap->length = round_up(length, 1 << blkbits);
+ iomap->type = IOMAP_MAPPED;
+ return 0;
+}
- bio = erofs_grab_raw_bio(sb, blkaddr, 1, true);
+static const struct iomap_ops erofs_meta_iomap_ops = {
+ .iomap_begin = erofs_meta_iomap_begin,
+};
- if (bio_add_page(bio, page, PAGE_SIZE, 0) != PAGE_SIZE) {
- err = -EFAULT;
- goto err_out;
- }
+static int
+erofs_meta_get_block(struct inode *inode, sector_t iblock,
+ struct buffer_head *bh, int create)
+{
+ bh->b_bdev = I_BDEV(inode);
+ bh->b_blocknr = iblock;
+ set_buffer_mapped(bh);
+ return 0;
+}
- submit_bio(bio);
- lock_page(page);
+static int erofs_read_meta_page(void *file, struct page *page)
+{
+ /* in case of getting some pages with buffer_heads */
+ if (i_blocksize(page->mapping->host) == PAGE_SIZE &&
+ !page_has_buffers(page))
+ return iomap_readpage(page, &erofs_meta_iomap_ops);
+
+ /*
+ * cannot use blkdev_readpage or blkdev_get_block directly
+ * since static in block_dev.c
+ */
+ return mpage_readpage(page, erofs_meta_get_block);
+}
- /* this page has been truncated by others */
- if (page->mapping != mapping) {
- unlock_page(page);
- put_page(page);
- goto repeat;
- }
+struct page *erofs_get_meta_page(struct super_block *sb, erofs_blk_t blkaddr)
+{
+ struct inode *const bd_inode = sb->s_bdev->bd_inode;
+ struct address_space *const mapping = bd_inode->i_mapping;
+ unsigned int nofs_flag;
+ struct page *page;
- /* more likely a read error */
- if (!PageUptodate(page)) {
- err = -EIO;
- goto err_out;
- }
- }
+ nofs_flag = memalloc_nofs_save();
+ page = read_cache_page(mapping, blkaddr, erofs_read_meta_page, NULL);
+ memalloc_nofs_restore(nofs_flag);
return page;
-
-err_out:
- unlock_page(page);
- put_page(page);
- return ERR_PTR(err);
}
static int erofs_map_blocks_flatmode(struct inode *inode,
--
2.17.1
