Re: 2.4.8-pre7: still buffer cache problems

[Ed Tomlinson <tomlins@cam.org>]

Hi Rik,

This has nice effects here.  With 320M memory starting a tob backup would put 
about 120M in the buffer cache.  With this applied it peaks at about 60M - the
system also remains more interactive.

If buffer_mem.borrow_percent is not used anywhere else suggest we reduce the
default percentage a bit more and see if things get even better.

Thoughts

Ed Tomlinson

On August 9, 2001 04:55 pm, Rik van Riel wrote:
> On Thu, 9 Aug 2001, marc heckmann wrote:
> > While 2.4.8-pre7 definitely fixes the "dd if=/dev/zero
> > of=bigfile bs=1000k count=bignumber" case. The "dd if=/dev/hda
> > of=/dev/null" is still quite broken for me.
>
> OK, there is no obvious way to do do drop-behind on
> buffer cache pages, but I think we can use a quick
> hack to make the system behave well under the presence
> of large amounts of buffer cache pages.
>
> What we could do is, in refill_inactive_scan(), just
> moving buffer cache pages to the inactive list regardless
> of page aging when there are too many buffercache pages
> around in the system.
>
> Does the patch below help you ?
>
> regards,
>
> Rik
> --
> IA64: a worthy successor to the i860.
>
> 		http://www.surriel.com/
> http://www.conectiva.com/	http://distro.conectiva.com/
>
>
> --- linux-2.4.7-ac7/mm/vmscan.c.buffer	Thu Aug  9 17:54:24 2001
> +++ linux-2.4.7-ac7/mm/vmscan.c	Thu Aug  9 17:55:09 2001
> @@ -708,6 +708,8 @@
>   * This function will scan a portion of the active list to find
>   * unused pages, those pages will then be moved to the inactive list.
>   */
> +#define too_many_buffers (atomic_read(&buffermem_pages) > \
> +		(num_physpages * buffer_mem.borrow_percent / 100))
>  int refill_inactive_scan(zone_t *zone, unsigned int priority, int target)
>  {
>  	struct list_head * page_lru;
> @@ -770,6 +772,18 @@
>  				page_active = 1;
>  			}
>  		}
> +
> +		/*
> +		 * If the amount of buffer cache pages is too
> +		 * high we just move every buffer cache page we
> +		 * find to the inactive list. Eventually they'll
> +		 * be reclaimed there...
> +		 */
> +		if (page->buffers && !page->mapping && too_many_buffers) {
> +			deactivate_page_nolock(page);
> +			page_active = 0;
> +		}
> +
>  		/*
>  		 * If the page is still on the active list, move it
>  		 * to the other end of the list. Otherwise we exit if
>
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