On Tue, Jul 31, 2018 at 11:04:05PM -0600, Chris Murphy wrote: > On Tue, Jul 31, 2018 at 10:41 PM, Eric Sandeen <sandeen@xxxxxxxxxxx> wrote: > > > > > > On 7/31/18 11:38 PM, Chris Murphy wrote: > >> On Tue, Jul 31, 2018 at 10:12 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote: > >>> On Tue, Jul 31, 2018 at 07:32:50PM -0600, Chris Murphy wrote: > >>>> This seems suboptimal. > >>> > >>> It's actually a very useful optimisation to make on thin devices. > >>> > >>>> Basically this is a 750G thin volume. I don't > >>>> have a plain partition on a device handy to try this out but I'm > >>>> pretty certain the default is 4 AG's in that case, so I'm confused why > >>>> by default 33 AGs are created on a thin volume. The LVM volume group > >>>> is on a dmcrypt PV. > >>> > >>> It's a thin volume, therefore it advertises an optimal IO size and > >>> alignment setting (i.e. the thin volume allocation chunk size). > >>> Hence mkfs.xfs treats it as a "multi-disk device" and sets up > >>> alignment and AG count appropriately. > >>> > >>> This is actually the right optimisation to make for sparse devices - > >>> more AGs increase filesystem concurrency but we normally restrict it > >>> on single spindles because each AG adds more seeks into typical > >>> workloads and slows them down. However, the thin volume already adds > >>> that penalty to the storage stack for us because they don't have a > >>> linear LBA-to-physical location characteristic. Hence we can > >>> increase filesystem concurrency without addition performance > >>> penalties being incurred. > >> > >> OK so why 33 AG's with xfsprogs 4.15, but 4 AG's with xfsprogs 4.17, > >> when directed to the same thin LV? And also the difference in sunit > >> and swidth? > >> > > > > Did you build 4.17 with --disable-blkid? > > Yep, that's what doc/INSTALL recommends. Removing that and rebuilding, > sure enough 33 AGs, sunit 128, swidth 1024, and sectsz 4096. I do get > a build time warning. Where did you see that --disable-blkid is recommended? Are you using MacOS to build it? > > Building mkfs > [CC] proto.o > [CC] xfs_mkfs.o > In function ‘finish_superblock_setup’, > inlined from ‘main’ at xfs_mkfs.c:3937:2: > xfs_mkfs.c:3188:3: warning: ‘strncpy’ specified bound 12 equals > destination size [-Wstringop-truncation] > strncpy(sbp->sb_fname, cfg->label, sizeof(sbp->sb_fname)); > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > [LD] mkfs.xfs > > > > -- > Chris Murphy > -- > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Carlos -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
