On Mon, 2011-01-03 at 09:40 +0200, Pekka Enberg wrote: > Hi, > > On Mon, Jan 3, 2011 at 8:48 AM, Theodore Ts'o <tytso@xxxxxxx> wrote: > >> Given the patches being busily submitted by trivial patch submitters to > >> make use kmem_cache_zalloc(), et. al, I believe we should remove the > >> unlikely() tests around the (gfp_flags & __GFP_ZERO) tests, such as: > >> > >> - if (unlikely((flags & __GFP_ZERO) && objp)) > >> + if ((flags & __GFP_ZERO) && objp) > >> memset(objp, 0, obj_size(cachep)); > >> > >> Agreed? If so, I'll send a patch... > > On Mon, Jan 3, 2011 at 5:46 AM, Minchan Kim <minchan.kim@xxxxxxxxx> wrote: > > I support it. > > I guess the rationale here is that if you're going to take the hit of > memset() you can take the hit of unlikely() as well. We're optimizing > for hot call-sites that allocate a small amount of memory and > initialize everything themselves. That said, I don't think the > unlikely() annotation matters much either way and am for removing it > unless people object to that. > > On Mon, Jan 3, 2011 at 5:46 AM, Minchan Kim <minchan.kim@xxxxxxxxx> wrote: > > Recently Steven tried to gather the information. > > http://thread.gmane.org/gmane.linux.kernel/1072767 > > Maybe he might have a number for that. > > That would be interesting, sure. Note, you could do it yourself too. Just enable: Kernel Hacking -> Tracers -> Branch Profiling (Trace likely/unlikely profiler) CONFIG_PROFILE_ANNOTATED_BRANCHES Then search /debug/tracing/trace_stats/branch_annotated. (hmm, the help in Kconfig is wrong, I need to fix that) Anyway, here's my box. I just started it an hour ago, and have not been doing too much on it yet. But here's what I got (using SLUB) correct incorrect % Function File Line ------- --------- - -------- ---- ---- 6890998 2784830 28 slab_alloc slub.c 1719 That's incorrect 28% of the time. -- Steve -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>