Readahead support for IOCB_NOWAIT was introduced in commit 2e85abf053b9
("mm: allow read-ahead with IOCB_NOWAIT set"). However, this behavior was
altered in commit efa8480a8316 ("fs: RWF_NOWAIT should imply IOCB_NOIO") to
prevent potential blocking during memory reclamation.
To address the blocking issue during memory reclamation, we can use
memalloc_nowait_{save,restore} to ensure non-blocking behavior. With this
change, we can restore the original functionality, allowing
preadv2(IOCB_NOWAIT) to read data directly from the disk if it's not
already in the page cache.
Link: https://lore.gnuweeb.org/io-uring/20200624164127.GP21350@xxxxxxxxxxxxxxxxxxxx/
Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
---
include/linux/fs.h | 1 -
mm/filemap.c | 6 ++++++
2 files changed, 6 insertions(+), 1 deletion(-)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index fd34b5755c0b..ced74b1b350d 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3455,7 +3455,6 @@ static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags,
if (flags & RWF_NOWAIT) {
if (!(ki->ki_filp->f_mode & FMODE_NOWAIT))
return -EOPNOTSUPP;
- kiocb_flags |= IOCB_NOIO;
}
if (flags & RWF_ATOMIC) {
if (rw_type != WRITE)
diff --git a/mm/filemap.c b/mm/filemap.c
index 657bcd887fdb..93c690e1d1fd 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -46,6 +46,7 @@
#include <linux/pipe_fs_i.h>
#include <linux/splice.h>
#include <linux/rcupdate_wait.h>
+#include <linux/sched/mm.h>
#include <asm/pgalloc.h>
#include <asm/tlbflush.h>
#include "internal.h"
@@ -2514,6 +2515,7 @@ static int filemap_get_pages(struct kiocb *iocb, size_t count,
pgoff_t index = iocb->ki_pos >> PAGE_SHIFT;
pgoff_t last_index;
struct folio *folio;
+ unsigned int flags;
int err = 0;
/* "last_index" is the index of the page beyond the end of the read */
@@ -2526,8 +2528,12 @@ static int filemap_get_pages(struct kiocb *iocb, size_t count,
if (!folio_batch_count(fbatch)) {
if (iocb->ki_flags & IOCB_NOIO)
return -EAGAIN;
+ if (iocb->ki_flags & IOCB_NOWAIT)
+ flags = memalloc_nowait_save();
page_cache_sync_readahead(mapping, ra, filp, index,
last_index - index);
+ if (iocb->ki_flags & IOCB_NOWAIT)
+ memalloc_nowait_restore(flags);
filemap_get_read_batch(mapping, index, last_index - 1, fbatch);
}
if (!folio_batch_count(fbatch)) {
--
2.43.5
