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Subject[RFC PATCH 2/2] erofs: directly traverse pages in z_erofs_readahead()
Date
In that way, pages can be accessed directly with xarray.

Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Gao Xiang <xiang@kernel.org>
---
Just an open-coded PoC one, since that is what EROFS actually needs but
without the iteration API (see [PATCH 1/2] as well.)

fs/erofs/zdata.c | 32 +++++++++++++-------------------
1 file changed, 13 insertions(+), 19 deletions(-)

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 054b9839e9db..210b2965ecc4 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -1416,7 +1416,8 @@ static void z_erofs_readahead(struct readahead_control *rac)
bool sync = (sbi->ctx.readahead_sync_decompress &&
nr_pages <= sbi->ctx.max_sync_decompress_pages);
struct z_erofs_decompress_frontend f = DECOMPRESS_FRONTEND_INIT(inode);
- struct page *page, *head = NULL;
+ struct page *page;
+ pgoff_t index;
LIST_HEAD(pagepool);

trace_erofs_readpages(inode, readahead_index(rac), nr_pages, false);
@@ -1434,26 +1435,19 @@ static void z_erofs_readahead(struct readahead_control *rac)
* 2) submission chain can be then in the forward order since
* pclusters are all inserted at head.
*/
- while ((page = readahead_page(rac))) {
- prefetchw(&page->flags);
-
- /*
- * A pure asynchronous readahead is indicated if
- * a PG_readahead marked page is hitted at first.
- * Let's also do asynchronous decompression for this case.
- */
- sync &= !(PageReadahead(page) && !head);
-
- set_page_private(page, (unsigned long)head);
- head = page;
- }
-
- while (head) {
- struct page *page = head;
+ index = rac->_index + rac->_nr_pages;
+ while (rac->_nr_pages) {
+ struct page *head;
int err;

- /* traversal in reverse order */
- head = (void *)page_private(page);
+ --rac->_nr_pages;
+ page = xa_load(&rac->mapping->i_pages, --index);
+ /* XXX: very incomplete thp support */
+ head = thp_head(page);
+ if (head != page) {
+ index -= page->index - head->index;
+ page = head;
+ }

err = z_erofs_do_read_page(&f, page, &pagepool);
if (err)
--
2.20.1
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