Date: Tue, 12 Sep 2000 11:53:56 -0400 (EDT) From: Christopher Stein <stein@eecs.harvard.edu> To: Marius Bendiksen <mbendiks@eunet.no> Cc: freebsd-fs@FreeBSD.ORG Subject: Re: how mmap buffer writes handled? Message-ID: <Pine.OSF.4.20.0009121146440.13225-100000@wally> In-Reply-To: <Pine.BSF.4.05.10009090805310.63380-100000@login-1.eunet.no>
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Yes, it appears to be done in vfs_setdirty() of kern/vfs_bio.c
Like so:
for (i = 0; i < bp->b_npages; i++) {
vm_page_flag_clear(bp->b_pages[i], PG_ZERO);
vm_page_test_dirty(bp->b_pages[i]);
}
My concern is that, for mmapped workloads, statistics like
nbuf and numdirtybuffers, which are used to set the
buf_daemon flush rate, will be meaningless as will the
clean and dirty buffer lists. vfs_setdirty is called
only from within bdwrite() (delayed write that writes from
applications into mmapped buffers will not transit through) and
vfs_busy_pages() (called before the physical device strategy
routine).
How are these data structures and statistics kept meaningful
under mmapped workloads?
thnx
-Chris
On Sat, 9 Sep 2000, Marius Bendiksen wrote:
> > dirtied by mmap moved onto the dirty queue? IS this done
> > synchronously by some kind of software intercept of the
> > page table operations or are the buffers moved from the
> > clean to dirty queues in the background?
>
> As I recall, a periodic scan of the "modified" bits of the various page
> table entries will be made, and the buffers will be dirtied accordingly
> as the scan completes.
>
> Marius
>
>
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