On 07/12/2012 07:01 AM, Dave Chinner wrote: > On Wed, Jul 11, 2012 at 11:55:34AM -0700, Hugh Dickins wrote: >> On Wed, 11 Jul 2012, Cong Wang wrote: >>> On Mon, 09 Jul 2012 at 22:41 GMT, Hugh Dickins <hughd@xxxxxxxxxx> wrote: >>>> Revert 4fb5ef089b28 ("tmpfs: support SEEK_DATA and SEEK_HOLE"). >>>> I believe it's correct, and it's been nice to have from rc1 to rc6; >>>> but as the original commit said: >>>> >>>> I don't know who actually uses SEEK_DATA or SEEK_HOLE, and whether it >>>> would be of any use to them on tmpfs. This code adds 92 lines and 752 >>>> bytes on x86_64 - is that bloat or worthwhile? >>> >>> >>> I don't think 752 bytes matter much, especially for x86_64. >>> >>>> >>>> Nobody asked for it, so I conclude that it's bloat: let's revert tmpfs >>>> to the dumb generic support for v3.5. We can always reinstate it later >>>> if useful, and anyone needing it in a hurry can just get it out of git. >>>> >>> >>> If you don't have burden to maintain it, I'd prefer to leave as it is, >>> I don't think 752-bytes is the reason we revert it. >> >> Thank you, your vote has been counted ;) >> and I'll be glad if yours stimulates some agreement or disagreement. >> >> 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 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. > > 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. :) 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>