Re: Helding the Kernel lock while doing IO???

[Andrea Arcangeli <andrea@suse.de>]

On 6 May 2000, Juan J. Quintela wrote:

>I am losing some detail?

kernel lock is released by schedule(). (the only problem of swapin are the
races with swapoff)

>diff -u -urN --exclude=CVS --exclude=*~ --exclude=.#* --exclude=TAGS pre7-6/ipc/shm.c testing2/ipc/shm.c
>--- pre7-6/ipc/shm.c	Fri May  5 23:58:56 2000
>+++ testing2/ipc/shm.c	Sat May  6 02:39:17 2000
>@@ -1379,10 +1379,11 @@
> 			if (!page) {
> 				lock_kernel();
> 				swapin_readahead(entry);
>-				page = read_swap_cache(entry);
>+				page = read_swap_cache_async(entry, 0);
> 				unlock_kernel();
> 				if (!page)
> 					goto oom;
>+                                wait_on_page(page);
> 			}
> 			delete_from_swap_cache(page);
> 			page = replace_with_highmem(page);
>diff -u -urN --exclude=CVS --exclude=*~ --exclude=.#* --exclude=TAGS pre7-6/mm/memory.c testing2/mm/memory.c
>--- pre7-6/mm/memory.c	Fri May  5 23:58:56 2000
>+++ testing2/mm/memory.c	Sat May  6 02:02:53 2000
>@@ -1038,11 +1038,10 @@
> 	if (!page) {
> 		lock_kernel();
> 		swapin_readahead(entry);
>-		page = read_swap_cache(entry);
>+		page = read_swap_cache_async(entry, 0);
> 		unlock_kernel();
> 		if (!page)
> 			return -1;
>-
> 		flush_page_to_ram(page);
> 		flush_icache_page(vma, page);
> 	}

The above patch would break swapin.

Andrea


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