From: Suparna Bhattacharya <suparna@in.ibm.com>
The open coded readahead logic which was added in aio_pread is best avoided
if possible. Duplicating similar checks across sync and aio paths (e.g.
checking for O_DIRECT) and the divergence of logic between these paths
isn't good from a long term maintainability standpoint.
Secondly, this logic really belongs in the generic fops methods for
aio_read rather than in the high level aio handlers; it should be possible
for a filesystem to override the logic with its own if suitable.
So, this patch moves the readahead out of aio_pread, and instead modifies
do_generic_mapping_read to readahead _all_ the pages in the range requested
upfront before it starts waiting for any of the pages to become uptodate.
This leads to sane readahead behaviour for the kind of i/o patterns
generated by streaming aio reads. It also takes care not to repeatedly
issue readaheads for subsequent AIO retries for the same request.
fs/aio.c | 19 +------------------
include/linux/aio.h | 3 +++
mm/filemap.c | 30 +++++++++++++++++++++++-------
3 files changed, 27 insertions(+), 25 deletions(-)
diff -puN fs/aio.c~aio-readahead-rework fs/aio.c
--- 25/fs/aio.c~aio-readahead-rework 2003-08-30 15:42:34.000000000 -0700
+++ 25-akpm/fs/aio.c 2003-08-30 15:42:34.000000000 -0700
@@ -1363,25 +1363,8 @@ ssize_t aio_setup_iocb(struct kiocb *kio
kiocb->ki_left)))
break;
ret = -EINVAL;
- if (file->f_op->aio_read) {
- /*
- * Do not do readahead for DIRECT i/o
- */
- if (!(file->f_flags & O_DIRECT)) {
- struct address_space *mapping;
- unsigned long index;
- unsigned long end;
-
- mapping = file->f_dentry->d_inode->i_mapping;
- index = kiocb->ki_pos >> PAGE_CACHE_SHIFT;
- end = (kiocb->ki_pos + kiocb->ki_left) >>
- PAGE_CACHE_SHIFT;
- for (; index < end; index++)
- page_cache_readahead(mapping,
- &file->f_ra, file, index);
- }
+ if (file->f_op->aio_read)
kiocb->ki_retry = aio_pread;
- }
break;
case IOCB_CMD_PWRITE:
ret = -EBADF;
diff -puN include/linux/aio.h~aio-readahead-rework include/linux/aio.h
--- 25/include/linux/aio.h~aio-readahead-rework 2003-08-30 15:42:34.000000000 -0700
+++ 25-akpm/include/linux/aio.h 2003-08-30 15:42:34.000000000 -0700
@@ -179,6 +179,9 @@ int FASTCALL(io_submit_one(struct kioctx
dump_stack(); \
}
+#define io_wait_to_kiocb(wait) container_of(wait, struct kiocb, ki_wait)
+#define is_retried_kiocb(iocb) ((iocb)->ki_retried > 1)
+
#include <linux/aio_abi.h>
static inline struct kiocb *list_kiocb(struct list_head *h)
diff -puN mm/filemap.c~aio-readahead-rework mm/filemap.c
--- 25/mm/filemap.c~aio-readahead-rework 2003-08-30 15:42:34.000000000 -0700
+++ 25-akpm/mm/filemap.c 2003-08-30 15:42:34.000000000 -0700
@@ -617,21 +617,39 @@ void do_generic_mapping_read(struct addr
read_actor_t actor)
{
struct inode *inode = mapping->host;
- unsigned long index, offset;
+ unsigned long index, offset, last, end_index;
struct page *cached_page;
+ loff_t isize = i_size_read(inode);
int error;
cached_page = NULL;
index = *ppos >> PAGE_CACHE_SHIFT;
offset = *ppos & ~PAGE_CACHE_MASK;
+ last = (*ppos + desc->count) >> PAGE_CACHE_SHIFT;
+ end_index = isize >> PAGE_CACHE_SHIFT;
+ if (last > end_index)
+ last = end_index;
+
+ /* Don't repeat the readahead if we are executing aio retries */
+ if (in_aio()) {
+ if (is_retried_kiocb(io_wait_to_kiocb(current->io_wait)))
+ goto done_readahead;
+ }
+
+ /*
+ * Let the readahead logic know upfront about all
+ * the pages we'll need to satisfy this request
+ */
+ for (; index < last; index++)
+ page_cache_readahead(mapping, ra, filp, index);
+ index = *ppos >> PAGE_CACHE_SHIFT;
+
+done_readahead:
for (;;) {
struct page *page;
- unsigned long end_index, nr, ret;
- loff_t isize = i_size_read(inode);
+ unsigned long nr, ret;
- end_index = isize >> PAGE_CACHE_SHIFT;
-
if (index > end_index)
break;
nr = PAGE_CACHE_SIZE;
@@ -642,8 +660,6 @@ void do_generic_mapping_read(struct addr
}
cond_resched();
- if (is_sync_wait(current->io_wait))
- page_cache_readahead(mapping, ra, filp, index);
nr = nr - offset;
find_page:
_