On 9/5/17 5:10 PM, Dave Chinner wrote: > On Tue, Sep 05, 2017 at 09:17:42AM -0500, Eric Sandeen wrote: >> >> >> On 9/5/17 1:44 AM, Dave Chinner wrote: >>> On Mon, Sep 04, 2017 at 11:31:39PM -0700, Christoph Hellwig wrote: >>>> On Tue, Sep 05, 2017 at 11:14:42AM +0530, Chandan Rajendra wrote: >>>>> Linux kernel commit 6c6b6f28b3335fd85ec833ee0005d9c9dca6c003 (loop: set >>>>> physical block size to PAGE_SIZE) now sets PAGE_SIZE as the default >>>>> physical sector size of loop devices. On ppc64, this causes loop devices >>>>> to have 64k as the physical sector size. >>>> >>>> Eek. We'll need to revert the loop change ASAP! >>> >>> And, FWIW, making the warning go away if probably a bad idea, >>> because XFS only supports devices with sector sizes up >>> to 32k: >> >> Well, TBH removing this warning was my suggestion, because it's >> automatically fixing values that weren't specified by the user in >> the first place. First preference is physical sector size, then >> fallback to logical but it doesn't need to be noisy about it. >> >>> #define XFS_MIN_SECTORSIZE_LOG 9 /* i.e. 512 bytes */ >>> #define XFS_MAX_SECTORSIZE_LOG 15 /* i.e. 32768 bytes */ >>> >>> And so it should be warning about devices trying to tell it to use >>> something larger.... >> >> As long as the logical sector size is small enough, it seems like a >> silent adjustment is probably ok, no? > > Think 512e drives. Doing 512 byte sector IO is possible, but slow. > Someone might actually want to avoid that by having the filesystem > use 4k sector sizes. However, if for some reason, mkfs selects 512 > byte sectors (the logical size) rather than 4k sector size, then > shouldn't we be telling the user we're doing something that has a > "for-the-life-of-the-filesystem" performance impact?
Well, sure, but it'll only select 512 if it /has/ to, i.e. if the block size is < 4k. So for the simple case of a 512e drive, our default block size is 4k, physical size is 4k, and everything is happy and fine. If the user /specifies/ a 1k block size on such a device, how much of a nanny do we really want to be about telling them this is suboptimal? There are a lot of suboptimal things you can specify on the mkfs commandline, but we don't generally choose to warn about them... -Eric > Cheers, > > Dave. >
