On Sun, Feb 18, 2018 at 09:28:30AM +0200, Andriy Gapon wrote: A> > A> vnode_pager_getpages_async() at vnode_pager_getpages_async+0x81/frame A> > A> 0xfffffe00b3c36650 A> > A> vn_sendfile() at vn_sendfile+0xe70/frame 0xfffffe00b3c368e0 A> > A> sendfile() at sendfile+0x149/frame 0xfffffe00b3c36980 A> > A> amd64_syscall() at amd64_syscall+0x79b/frame 0xfffffe00b3c36ab0 A> > A> fast_syscall_common() at fast_syscall_common+0x101/frame 0x7fffffffdb00 A> > A> A> > A> I looked at sendfile_swapin() code and it seems that it uses the pager API in an A> > A> undocumented way. Specifically, it inserts bogus_page into the array of A> > A> requested pages. For starters, bogus_page is not busied and VOP_GETPAGES is A> > A> documented to have all requested pages exclusively busied. Second, I always had A> > A> an impression that bogus_page is an implementation detail of the unified buffer A> > A> / page cache and that other code need not be aware of it. A> > A> A> > A> So, my opinion is that the sendfile code uses a "clever hack" that happens to A> > A> work with the buffer cache based filesystems, but that that hack is a bug. A> > A> So, I'd prefer that the problem is fixed in that code. A> > A> But I am open to being convinced that all VOP_GETPAGES implementations, A> > A> including that in ZFS, must be made aware of bogus_page. Or, at least, that A> > A> they should not verify that the requested pages are busied. A> > A> > This is optimization that improves throughput when file memory cache is A> > fragmented. Why don't you like adding the code to zfs_freebsd_getpages()? A> A> I cited two reasons above and expected to hear some counter-points rather than A> them being ignored :-) A> If we settle upon allowing bogus_page to be used in ma, then that will A> obviously need to be documented.
My only point is that it is a performance improvement. IMHO that's enough :) If you can't suggest a more elegant way of doing that improvement, then all I can suggest is to document it and add its support to ZFS. -- Gleb Smirnoff _______________________________________________ firstname.lastname@example.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-current To unsubscribe, send any mail to "freebsd-current-unsubscr...@freebsd.org"