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SubjectRe: [PATCH] swapin flush cache bug
Hello Marcelo, 

This is follow-up to the mail in February. You may perhaps forget the
context, it's the bug of MM about cache flushing for swapped-in-pages.
I see this bug on SuperH port (SH-4).

I think that we have this issue on the machine whose flush_dcache_page()
is defined. In current code, the cache aren't flushed for
the asynchronously-swapped-in pages which is cached in swap cache.
This is the problem.

Marcelo Tosatti writes:
> Yet another thing (1) on end_buffer_io_async() to handle a case which is
> only true for a specific user of it. Since the other special case handling
> is for swap IO too, I think a separate IO end operation for swap would be
> interesting.
>
> (1) The current one is SetPageDecrAfter handling.

How about this? I've updated MM bugzilla already.

2001-06-26 NIIBE Yutaka <gniibe@m17n.org>

* include/linux/mm.h (PG_flush_after, PageFlushAfter,
SetPageFlushAfter, PageTestandClearFlushAfter): New bit.
* mm/page_io.c (rw_swap_page_base): Set flush-after bit.
* fs/buffer.c (end_buffer_io_async): Implement flush-ing
with PG_flush_after.

* mm/memory.c (do_swap_page): Remove flush-ing the page.

diff -ruNp --exclude=CVS --exclude=.cvsignore v2.4.6-pre5/fs/buffer.c kernel/fs/buffer.c
--- v2.4.6-pre5/fs/buffer.c Mon Jun 25 18:48:07 2001
+++ kernel/fs/buffer.c Tue Jun 26 15:11:17 2001
@@ -831,6 +831,9 @@ static void end_buffer_io_async(struct b
if (PageTestandClearDecrAfter(page))
atomic_dec(&nr_async_pages);

+ if (PageTestandClearFlushAfter(page))
+ flush_dcache_page(page);
+
UnlockPage(page);

return;
diff -ruNp --exclude=CVS --exclude=.cvsignore v2.4.6-pre5/include/linux/mm.h kernel/include/linux/mm.h
--- v2.4.6-pre5/include/linux/mm.h Mon Jun 25 18:48:09 2001
+++ kernel/include/linux/mm.h Tue Jun 26 14:58:56 2001
@@ -282,6 +282,7 @@ typedef struct page {
#define PG_inactive_clean 11
#define PG_highmem 12
#define PG_checked 13 /* kill me in 2.5.<early>. */
+#define PG_flush_after 14
/* bits 21-29 unused */
#define PG_arch_1 30
#define PG_reserved 31
@@ -364,6 +365,10 @@ static inline void set_page_dirty(struct

#define SetPageReserved(page) set_bit(PG_reserved, &(page)->flags)
#define ClearPageReserved(page) clear_bit(PG_reserved, &(page)->flags)
+
+#define PageFlushAfter(page) test_bit(PG_flush_after, &(page)->flags)
+#define SetPageFlushAfter(page) set_bit(PG_flush_after, &(page)->flags)
+#define PageTestandClearFlushAfter(page) test_and_clear_bit(PG_flush_after, &(page)->flags)

/*
* Error return values for the *_nopage functions
diff -ruNp --exclude=CVS --exclude=.cvsignore v2.4.6-pre5/mm/memory.c kernel/mm/memory.c
--- v2.4.6-pre5/mm/memory.c Mon Jun 25 18:48:10 2001
+++ kernel/mm/memory.c Tue Jun 26 14:48:15 2001
@@ -1109,8 +1109,6 @@ static int do_swap_page(struct mm_struct
return -1;
}
wait_on_page(page);
- flush_page_to_ram(page);
- flush_icache_page(vma, page);
}

/*
diff -ruNp --exclude=CVS --exclude=.cvsignore v2.4.6-pre5/mm/page_io.c kernel/mm/page_io.c
--- v2.4.6-pre5/mm/page_io.c Mon Apr 30 16:15:32 2001
+++ kernel/mm/page_io.c Tue Jun 26 15:01:00 2001
@@ -50,6 +50,7 @@ static int rw_swap_page_base(int rw, swp

if (rw == READ) {
ClearPageUptodate(page);
+ SetPageFlushAfter(page);
kstat.pswpin++;
} else
kstat.pswpout++;
--
-
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