On Mon, Feb 20, 2017 at 11:42:31AM -0500, Chuck Lever wrote: > > > On Feb 20, 2017, at 11:09 AM, J. Bruce Fields <bfields@xxxxxxxxxx> wrote: > > > > On Sun, Feb 19, 2017 at 02:29:03PM -0500, Chuck Lever wrote: > >> > >>> On Feb 18, 2017, at 9:07 PM, J. Bruce Fields <bfields@xxxxxxxxxx> wrote: > >>> > >>> From: Weston Andros Adamson <dros@xxxxxxxxxx> > >>> > >>> Instead of preallocating pags, allow xdr_partial_copy_from_skb() to > >>> allocate whatever pages we need on demand. This is what the NFSv3 ACL > >>> code does. > >> > >> The patch description does not explain why this change is > >> being done. > > > > The only justification I see is avoiding allocating pages unnecessarily. > > That makes sense. Is there a real world workload that has seen > a negative effect? > > > > Without this patch, for each getacl, we allocate 17 pages (if I'm > > calculating correctly) and probably rarely use most of them. > > > > In the v3 case I think it's 7 pages instead of 17. > > I would have guessed 9. Out of curiosity, is there a reason > documented for these size limits? In the v4 case: #define NFS4ACL_MAXPAGES DIV_ROUND_UP(XATTR_SIZE_MAX, PAGE_SIZE) And I believe XATTR_SIZE_MAX is a global maximum on the size of any extend attribute value. In the v3 case: /* Maximum number of ACL entries over NFS */ #define NFS_ACL_MAX_ENTRIES 1024 #define NFSACL_MAXPAGES ((2*(8+12*NFS_ACL_MAX_ENTRIES) + PAGE_SIZE-1) \ >> PAGE_SHIFT) No idea where that 1024 comes from. --b. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
