Re: [f2fs-dev] [PATCH v11 19/25] erofs: Convert compressed files from readpages to readahead
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 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
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Re: [f2fs-dev] [PATCH v11 19/25] erofs: Convert compressed files from readpages to readahead
On Tue, 14 Apr 2020 08:02:27 -0700 Matthew Wilcox 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?
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[f2fs-dev] [PATCH v11 19/25] erofs: Convert compressed files from readpages to readahead
From: "Matthew Wilcox (Oracle)"
Use the new readahead operation in erofs.
Signed-off-by: Matthew Wilcox (Oracle)
Acked-by: Gao Xiang
Reviewed-by: Dave Chinner
Reviewed-by: William Kucharski
Reviewed-by: Chao Yu
---
fs/erofs/zdata.c | 29 +
1 file changed, 9 insertions(+), 20 deletions(-)
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,
};
--
2.25.1
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