On 07/16/2012 05:28 PM, Hugh Dickins wrote: > On Thu, 12 Jul 2012, Jeff Liu wrote: >> On 07/12/2012 07:01 AM, Dave Chinner wrote: >>> On Wed, Jul 11, 2012 at 11:55:34AM -0700, Hugh Dickins wrote: >>>> >>>> But your vote would count for a lot more if you know of some app which >>>> would really benefit from this functionality in tmpfs: I've heard of none. >>> >>> So what? I've heard of no apps that use this functionality on XFS, >>> either, but I have heard of a lot of people asking for it to be >>> implemented over the past couple of years so they can use it. >>> There's been patches written to make coreutils (cp) make use of it >>> instead of parsing FIEMAP output to find holes, though I don't know >>> if that's gone beyond more than "here's some patches"... >> >> Yes, for apps, cp(1) will make use of it to replace the old FIEMAP for efficient sparse file copy. >> I have implemented an extent-scan module to coreutils a few years ago, >> http://fossies.org/dox/coreutils-8.17/extent-scan_8c_source.html > > Thanks for confirming Dave's pointer to cp. > > Of course, tmpfs has never supported FIBMAP or FIEMAP; > but SEEK_DATA and SEEK_HOLE do fit it much more naturally. > >> >> It does extent scan through FIEMAP, however, SEEK_DATA/SEEK_HOLE is more convenient and easy to use >> considering the call interface. So FIEMAP will be replaced by SEEK_XXX once it got supported by EXT4. >> >> Moreover, I have discussed with Jim who is the coreutils maintainer previously, He would like to post >> extent-scan module to Gnulib so that other GNU utilities which are relied on Gnulib might be a potential >> user of it, at least, GNU tar will definitely need it for sparse file backup. > > Thanks for the info. I confess I'm not hugely swayed by cp and sparse > file archive arguments - I doubt many people care, and I doubt those who > do care are using tmpfs for them. > > But my doubts are just ignorance. I was hoping to hear, not that we have > tools to copy sparse files efficiently (umm, over the network?), but > what apps are actually working live with those sparse files on tmpfs, > and now need to seek around them. Some math or physics applications? > >>> >>> Besides, given that you can punch holes in tmpfs files, it seems >>> strange to then say "we don't need a method of skipping holes to >>> find data quickly".... >> >> So its deserve to keep this feature working on tmpfs considering hole punch. :) > > Well, thank you, as I said earlier I am on both sides of the argument. > (And feel uncomfortably like a prima donna waiting in the wings until > the audience has shouted long enough for the encore.) Oh, sorry, I missed you response to Dave before. > > It's now taken out of 3.5, but we can bring it back when there's more > demand. Yep. :) Thanks, -Jeff > Your extent-scan is itself waiting for ext4 to support it: > maybe get noisy at me when that's imminent. > > Hugh > >> >> Thanks, >> -Jeff >> >>> >>> Besides, seek-hole/data is still shiny new and lots of developers >>> aren't even aware of it's presence in recent kernels. Removing new >>> functionality saying "no-one is using it" is like smashing the egg >>> before the chicken hatches (or is it cutting of the chickes's head >>> before it lays the egg?). >>> >>> Cheers, >>> >>> Dave. > -- > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
