[linux-lvm] PATCH: bdi_congested-core.patch (was: Re: IO scheduler, queue depth, nr_requests)

[Miquel van Smoorenburg <miquels@cistron.nl>]

According to Jens Axboe:
> On Thu, Feb 26 2004, Andrew Morton wrote:
> > Miquel van Smoorenburg <miquels@cistron.nl> wrote:
> > > Well, I'm looking for guidance from Jens first, since I'm not sure if
> > > he wants the first solution (congestion testing passed down), the second
> > > (congestion setting passed up) or both.
> > 
> > The first patch looks nice.  Why do we need the "pass it up" feature?
> 
> Miquel, the newer patches do tend to get too complicated. I suppose I'm
> fine with the first patch as well, modulo the dm part (I'd suggest
> merging it without and talking to Joe about doing it properly).

Okay here you go. I added bdi_rw_congested() for code in xfs and ext2
that calls both bdi_read_congested() and bdi_write_congested() in
a row, and it was "free" anyway.

bdi_congested-core.patch

--- linux-2.6.3.orig/include/linux/backing-dev.h	2004-02-04 04:43:38.000000000 +0100
+++ linux-2.6.3-congested_fn/include/linux/backing-dev.h	2004-02-26 16:17:49.000000000 +0100
@@ -20,10 +20,14 @@ enum bdi_state {
 	BDI_unused,		/* Available bits start here */
 };
 
+typedef int (congested_fn)(void *, int);
+
 struct backing_dev_info {
 	unsigned long ra_pages;	/* max readahead in PAGE_CACHE_SIZE units */
 	unsigned long state;	/* Always use atomic bitops on this */
 	int memory_backed;	/* Cannot clean pages with writepage */
+	congested_fn *congested_fn; /* Function pointer if device is md/dm */
+	void *congested_data;	/* Pointer to aux data for congested func */
 };
 
 extern struct backing_dev_info default_backing_dev_info;
@@ -32,14 +36,27 @@ int writeback_acquire(struct backing_dev
 int writeback_in_progress(struct backing_dev_info *bdi);
 void writeback_release(struct backing_dev_info *bdi);
 
+static inline int bdi_congested(struct backing_dev_info *bdi, int bdi_bits)
+{
+	if (bdi->congested_fn)
+		return bdi->congested_fn(bdi->congested_data, bdi_bits);
+	return (bdi->state & bdi_bits);
+}
+
 static inline int bdi_read_congested(struct backing_dev_info *bdi)
 {
-	return test_bit(BDI_read_congested, &bdi->state);
+	return bdi_congested(bdi, 1 << BDI_read_congested);
 }
 
 static inline int bdi_write_congested(struct backing_dev_info *bdi)
 {
-	return test_bit(BDI_write_congested, &bdi->state);
+	return bdi_congested(bdi, 1 << BDI_write_congested);
+}
+
+static inline int bdi_rw_congested(struct backing_dev_info *bdi)
+{
+	return bdi_congested(bdi, (1 << BDI_read_congested)|
+				  (1 << BDI_write_congested));
 }
 
 #endif		/* _LINUX_BACKING_DEV_H */