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SubjectRe: [Patch 2/2] Retry based aio read - filesystem read changes
On Wed, Mar 05, 2003 at 02:47:54PM +0530, Suparna Bhattacharya wrote:
> For the last few days I've been playing with prototyping
> a particular flavour of a retry based implementation for
> filesystem aio read.

# aioread.patch : Modifications for aio read in
# particular (generic_file_aio_read)


diff -ur linux-2.5.62/include/linux/pagemap.h linux-2.5.62-aio/include/linux/pagemap.h
--- linux-2.5.62/include/linux/pagemap.h Tue Feb 18 04:25:49 2003
+++ linux-2.5.62-aio/include/linux/pagemap.h Thu Feb 27 19:01:39 2003
@@ -93,6 +93,16 @@
if (TestSetPageLocked(page))
__lock_page(page);
}
+
+extern int FASTCALL(__aio_lock_page(struct page *page));
+static inline int aio_lock_page(struct page *page)
+{
+ if (TestSetPageLocked(page))
+ return __aio_lock_page(page);
+ else
+ return 0;
+}
+

/*
* This is exported only for wait_on_page_locked/wait_on_page_writeback.
@@ -113,6 +123,15 @@
wait_on_page_bit(page, PG_locked);
}

+extern int FASTCALL(aio_wait_on_page_bit(struct page *page, int bit_nr));
+static inline int aio_wait_on_page_locked(struct page *page)
+{
+ if (PageLocked(page))
+ return aio_wait_on_page_bit(page, PG_locked);
+ else
+ return 0;
+}
+
/*
* Wait for a page to complete writeback
*/
diff -ur linux-2.5.62/mm/filemap.c linux-2.5.62-aio/mm/filemap.c
--- linux-2.5.62/mm/filemap.c Tue Feb 18 04:26:11 2003
+++ linux-2.5.62-aio/mm/filemap.c Mon Mar 3 19:32:40 2003
@@ -268,6 +268,43 @@
}
EXPORT_SYMBOL(wait_on_page_bit);

+int aio_schedule(void)
+{
+ if (!current->iocb) {
+ io_schedule();
+ return 0;
+ } else {
+ pr_debug("aio schedule");
+ return -EIOCBQUEUED;
+ }
+}
+
+int aio_wait_on_page_bit(struct page *page, int bit_nr)
+{
+ wait_queue_head_t *waitqueue = page_waitqueue(page);
+ DEFINE_WAIT(sync_wait);
+ wait_queue_t *wait = &sync_wait;
+ int state = TASK_UNINTERRUPTIBLE;
+
+ if (current->iocb) {
+ wait = &current->iocb->ki_wait;
+ state = TASK_RUNNING;
+ }
+
+ do {
+ prepare_to_wait(waitqueue, wait, state);
+ if (test_bit(bit_nr, &page->flags)) {
+ sync_page(page);
+ if (-EIOCBQUEUED == aio_schedule())
+ return -EIOCBQUEUED;
+ }
+ } while (test_bit(bit_nr, &page->flags));
+ finish_wait(waitqueue, wait);
+
+ return 0;
+}
+EXPORT_SYMBOL(aio_wait_on_page_bit);
+
/**
* unlock_page() - unlock a locked page
*
@@ -336,6 +373,31 @@
}
EXPORT_SYMBOL(__lock_page);

+int __aio_lock_page(struct page *page)
+{
+ wait_queue_head_t *wqh = page_waitqueue(page);
+ DEFINE_WAIT(sync_wait);
+ wait_queue_t *wait = &sync_wait;
+ int state = TASK_UNINTERRUPTIBLE;
+
+ if (current->iocb) {
+ wait = &current->iocb->ki_wait;
+ state = TASK_RUNNING;
+ }
+
+ while (TestSetPageLocked(page)) {
+ prepare_to_wait(wqh, wait, state);
+ if (PageLocked(page)) {
+ sync_page(page);
+ if (-EIOCBQUEUED == aio_schedule())
+ return -EIOCBQUEUED;
+ }
+ }
+ finish_wait(wqh, wait);
+ return 0;
+}
+EXPORT_SYMBOL(__aio_lock_page);
+
/*
* a rather lightweight function, finding and getting a reference to a
* hashed page atomically.
@@ -614,7 +676,13 @@
goto page_ok;

/* Get exclusive access to the page ... */
- lock_page(page);
+
+ if (aio_lock_page(page)) {
+ pr_debug("queued lock page \n");
+ error = -EIOCBQUEUED;
+ /* TBD: should we hold on to the cached page ? */
+ goto sync_error;
+ }

/* Did it get unhashed before we got the lock? */
if (!page->mapping) {
@@ -636,12 +704,18 @@
if (!error) {
if (PageUptodate(page))
goto page_ok;
- wait_on_page_locked(page);
+ if (aio_wait_on_page_locked(page)) {
+ pr_debug("queued wait_on_page \n");
+ error = -EIOCBQUEUED;
+ /*TBD:should we hold on to the cached page ?*/
+ goto sync_error;
+ }
if (PageUptodate(page))
goto page_ok;
error = -EIO;
}

+sync_error:
/* UHHUH! A synchronous read error occurred. Report it */
desc->error = error;
page_cache_release(page);
@@ -813,6 +887,7 @@
ssize_t ret;

init_sync_kiocb(&kiocb, filp);
+ BUG_ON(current->iocb != NULL);
ret = __generic_file_aio_read(&kiocb, &local_iov, 1, ppos);
if (-EIOCBQUEUED == ret)
ret = wait_on_sync_kiocb(&kiocb);
@@ -844,6 +919,7 @@
{
read_descriptor_t desc;

+ BUG_ON(current->iocb != NULL);
if (!count)
return 0;

-
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