On Mon, Oct 31, 2016 at 05:02:46PM -0700, Gleb Smirnoff wrote: > Hi, > > On Fri, Oct 28, 2016 at 11:43:59AM +0000, Konstantin Belousov wrote: > K> Author: kib > K> Date: Fri Oct 28 11:43:59 2016 > K> New Revision: 308026 > K> URL: https://svnweb.freebsd.org/changeset/base/308026 > K> > K> Log: > K> Generalize UFS buffer pager to allow it serving other filesystems > K> which also use buffer cache. > K> > K> Most important addition to the code is the handling of filesystems > K> where the block size is less than the machine page size, which might > K> require reading several buffers to validate single page. > K> > K> Tested by: pho > K> Sponsored by: The FreeBSD Foundation > K> MFC after: 2 weeks > K> > K> Modified: > K> head/sys/kern/vfs_bio.c > K> head/sys/sys/buf.h > K> head/sys/ufs/ffs/ffs_vnops.c > K> > K> Modified: head/sys/kern/vfs_bio.c > K> > ============================================================================== > K> --- head/sys/kern/vfs_bio.c Fri Oct 28 11:35:06 2016 > (r308025) > K> +++ head/sys/kern/vfs_bio.c Fri Oct 28 11:43:59 2016 > (r308026) > K> @@ -75,9 +75,10 @@ __FBSDID("$FreeBSD$"); > K> #include <vm/vm.h> > K> #include <vm/vm_param.h> > K> #include <vm/vm_kern.h> > K> -#include <vm/vm_pageout.h> > K> -#include <vm/vm_page.h> > K> #include <vm/vm_object.h> > K> +#include <vm/vm_page.h> > K> +#include <vm/vm_pageout.h> > K> +#include <vm/vm_pager.h> > K> #include <vm/vm_extern.h> > K> #include <vm/vm_map.h> > K> #include <vm/swap_pager.h> > K> @@ -4636,6 +4637,161 @@ bdata2bio(struct buf *bp, struct bio *bi > K> } > K> } > K> > K> +static int buf_pager_relbuf; > K> +SYSCTL_INT(_vfs, OID_AUTO, buf_pager_relbuf, CTLFLAG_RWTUN, > K> + &buf_pager_relbuf, 0, > K> + "Make buffer pager release buffers after reading"); > K> + > K> +/* > K> + * The buffer pager. It uses buffer reads to validate pages. > K> + * > K> + * In contrast to the generic local pager from vm/vnode_pager.c, this > K> + * pager correctly and easily handles volumes where the underlying > K> + * device block size is greater than the machine page size. The > K> + * buffer cache transparently extends the requested page run to be > K> + * aligned at the block boundary, and does the necessary bogus page > K> + * replacements in the addends to avoid obliterating already valid > K> + * pages. > K> + * > K> + * The only non-trivial issue is that the exclusive busy state for > K> + * pages, which is assumed by the vm_pager_getpages() interface, is > K> + * incompatible with the VMIO buffer cache's desire to share-busy the > K> + * pages. This function performs a trivial downgrade of the pages' > K> + * state before reading buffers, and a less trivial upgrade from the > K> + * shared-busy to excl-busy state after the read. > > IMHO, should be noted that the pager ignores requested rbehind and rahead > values, and does the rbehind and rahead sizes that he prefers. Pager interface considers the ahead/behind pages' page-in as unsignificant, in particular because the pages can be recycled or invalidated during the pager operation, when pager drops the object lock.
More important, this pager de-facto uses the optimal filesystem-depended aligned io size due to its structure, comparing with the bmap pager. For this reason, I consider additional attempts to follow optional upper-level hints not very useful. Measurements show no difference in the real workload times, and marginal improvements for microbenchmarks (5% scale). I might do something more aggressive when upper-level specified rahead is (significantly) above the natural block size limit, like using breadn() instead of bread(). Practice suggests that this would not help or even be a pessimisation due to higher buf cache trashing. _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
