diff mbox series

[v11,19/25] erofs: Convert compressed files from readpages to readahead

Message ID 20200414150233.24495-20-willy@infradead.org (mailing list archive)
State New, archived
Headers show
Series Change readahead API | expand

Commit Message

Matthew Wilcox April 14, 2020, 3:02 p.m. UTC 
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

Use the new readahead operation in erofs.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Gao Xiang <gaoxiang25@huawei.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
---
 fs/erofs/zdata.c | 29 +++++++++--------------------
 1 file changed, 9 insertions(+), 20 deletions(-)

Comments

Andrew Morton April 21, 2020, 5:42 a.m. UTC | #1 
On Tue, 14 Apr 2020 08:02:27 -0700 Matthew Wilcox <willy@infradead.org> wrote:

> 
> Use the new readahead operation in erofs.
> 

Well this is exciting.

fs/erofs/data.c: In function erofs_raw_access_readahead:
fs/erofs/data.c:149:18: warning: last_block may be used uninitialized in this function [-Wmaybe-uninitialized]
	*last_block + 1 != current_block) {

It seems to be a preexisting bug, which your patch prompted gcc-7.2.0
to notice.

erofs_read_raw_page() goes in and uses *last_block, but neither of its
callers has initialized it.  Could the erofs maintainers please take a
look?
Gao Xiang April 21, 2020, 7:28 a.m. UTC | #2 
Hi Andrew,

On Mon, Apr 20, 2020 at 10:42:10PM -0700, Andrew Morton wrote:
> On Tue, 14 Apr 2020 08:02:27 -0700 Matthew Wilcox <willy@infradead.org> wrote:
> 
> > 
> > Use the new readahead operation in erofs.
> > 
> 
> Well this is exciting.
> 
> fs/erofs/data.c: In function erofs_raw_access_readahead:
> fs/erofs/data.c:149:18: warning: last_block may be used uninitialized in this function [-Wmaybe-uninitialized]
> 	*last_block + 1 != current_block) {
> 
> It seems to be a preexisting bug, which your patch prompted gcc-7.2.0
> to notice.
> 
> erofs_read_raw_page() goes in and uses *last_block, but neither of its
> callers has initialized it.  Could the erofs maintainers please take a
> look?

simply because last_block doesn't need to be initialized at first,
because bio == NULL in the begining anyway. I believe this is a gcc
false warning because some gcc versions raised some before (many gccs
don't, including my current gcc (Debian 8.3.0-6) 8.3.0).

in detail,

146         /* note that for readpage case, bio also equals to NULL */
147         if (bio &&
148             /* not continuous */
149             *last_block + 1 != current_block) {
150 submit_bio_retry:
151                 submit_bio(bio);
152                 bio = NULL;
153         }

bio will be NULL and will bypass the next condition at first.
after that,

155         if (!bio) {

...

221                 bio = bio_alloc(GFP_NOIO, nblocks);

...

}

...

230         err = bio_add_page(bio, page, PAGE_SIZE, 0);
231         /* out of the extent or bio is full */
232         if (err < PAGE_SIZE)
233                 goto submit_bio_retry;
234
235         *last_block = current_block;

so bio != NULL, and last_block will be assigned then as well.

Thanks,
Gao Xiang
diff mbox series

Patch

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index a78108128af3..187f93b4900e 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -1305,28 +1305,23 @@  static bool should_decompress_synchronously(struct erofs_sb_info *sbi,
 	return nr <= sbi->max_sync_decompress_pages;
 }
 
-static int z_erofs_readpages(struct file *filp, struct address_space *mapping,
-			     struct list_head *pages, unsigned int nr_pages)
+static void z_erofs_readahead(struct readahead_control *rac)
 {
-	struct inode *const inode = mapping->host;
+	struct inode *const inode = rac->mapping->host;
 	struct erofs_sb_info *const sbi = EROFS_I_SB(inode);
 
-	bool sync = should_decompress_synchronously(sbi, nr_pages);
+	bool sync = should_decompress_synchronously(sbi, readahead_count(rac));
 	struct z_erofs_decompress_frontend f = DECOMPRESS_FRONTEND_INIT(inode);
-	gfp_t gfp = mapping_gfp_constraint(mapping, GFP_KERNEL);
-	struct page *head = NULL;
+	struct page *page, *head = NULL;
 	LIST_HEAD(pagepool);
 
-	trace_erofs_readpages(mapping->host, lru_to_page(pages)->index,
-			      nr_pages, false);
+	trace_erofs_readpages(inode, readahead_index(rac),
+			readahead_count(rac), false);
 
-	f.headoffset = (erofs_off_t)lru_to_page(pages)->index << PAGE_SHIFT;
-
-	for (; nr_pages; --nr_pages) {
-		struct page *page = lru_to_page(pages);
+	f.headoffset = readahead_pos(rac);
 
+	while ((page = readahead_page(rac))) {
 		prefetchw(&page->flags);
-		list_del(&page->lru);
 
 		/*
 		 * A pure asynchronous readahead is indicated if
@@ -1335,11 +1330,6 @@  static int z_erofs_readpages(struct file *filp, struct address_space *mapping,
 		 */
 		sync &= !(PageReadahead(page) && !head);
 
-		if (add_to_page_cache_lru(page, mapping, page->index, gfp)) {
-			list_add(&page->lru, &pagepool);
-			continue;
-		}
-
 		set_page_private(page, (unsigned long)head);
 		head = page;
 	}
@@ -1368,11 +1358,10 @@  static int z_erofs_readpages(struct file *filp, struct address_space *mapping,
 
 	/* clean up the remaining free pages */
 	put_pages_list(&pagepool);
-	return 0;
 }
 
 const struct address_space_operations z_erofs_aops = {
 	.readpage = z_erofs_readpage,
-	.readpages = z_erofs_readpages,
+	.readahead = z_erofs_readahead,
 };