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SubjectRe: dirty balancing deadlock
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> Solves the FUSE deadlock, but not the throttle_vm_writeout() one.
> I'll try to tackle that one as well.
>
> If the per-bdi dirty counter goes below 16, balance_dirty_pages()
> returns.
>
> Does the constant need to tunable? If it's too large, then the global
> threshold is more easily exceeded. If it's too small, then in a tight
> situation progress will be slower.

Similar in spirit, this should solve the deadlock on throttle_vm_writeout().
Totally untested.

Does this approach look workable?

Thanks,
Miklos


Index: linux/include/linux/swap.h
===================================================================
--- linux.orig/include/linux/swap.h 2007-02-19 23:39:36.000000000 +0100
+++ linux/include/linux/swap.h 2007-02-20 00:03:38.000000000 +0100
@@ -277,10 +277,14 @@ static inline void disable_swap_token(vo
put_swap_token(swap_token_mm);
}

+#define nr_swap_writeback \
+ atomic_long_read(&swapper_space.backing_dev_info->nr_writeback)
+
#else /* CONFIG_SWAP */

#define total_swap_pages 0
#define total_swapcache_pages 0UL
+#define nr_swap_writeback 0UL

#define si_swapinfo(val) \
do { (val)->freeswap = (val)->totalswap = 0; } while (0)
Index: linux/mm/page-writeback.c
===================================================================
--- linux.orig/mm/page-writeback.c 2007-02-19 23:43:03.000000000 +0100
+++ linux/mm/page-writeback.c 2007-02-20 00:03:49.000000000 +0100
@@ -33,6 +33,7 @@
#include <linux/syscalls.h>
#include <linux/buffer_head.h>
#include <linux/pagevec.h>
+#include <linux/swap.h>

/*
* The maximum number of pages to writeout in a single bdflush/kupdate
@@ -332,6 +333,9 @@ void throttle_vm_writeout(void)
if (global_page_state(NR_UNSTABLE_NFS) +
global_page_state(NR_WRITEBACK) <= dirty_thresh)
break;
+
+ if (nr_swap_writeback < 16)
+ break;
congestion_wait(WRITE, HZ/10);
}
}
Index: linux/mm/page_io.c
===================================================================
--- linux.orig/mm/page_io.c 2007-02-19 23:24:23.000000000 +0100
+++ linux/mm/page_io.c 2007-02-19 23:42:21.000000000 +0100
@@ -70,6 +70,7 @@ static int end_swap_bio_write(struct bio
ClearPageReclaim(page);
}
end_page_writeback(page);
+ atomic_long_dec(&swapper_space.backing_dev_info->nr_writeback);
bio_put(bio);
return 0;
}
@@ -121,6 +122,7 @@ int swap_writepage(struct page *page, st
if (wbc->sync_mode == WB_SYNC_ALL)
rw |= (1 << BIO_RW_SYNC);
count_vm_event(PSWPOUT);
+ atomic_long_inc(&swapper_space.backing_dev_info->nr_writeback);
set_page_writeback(page);
unlock_page(page);
submit_bio(rw, bio);
-
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