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Date: Mon, 3 Jan 2011 09:40:57 +0200 From: Pekka Enberg <penberg@...nel.org> To: Minchan Kim <minchan.kim@...il.com> Cc: "Theodore Ts'o" <tytso@....edu>, Christoph Lameter <cl@...ux-foundation.org>, Pekka Enberg <penberg@...helsinki.fi>, Matt Mackall <mpm@...enic.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>, David Rientjes <rientjes@...gle.com>, npiggin@...nel.dk Subject: Re: Should we be using unlikely() around tests of GFP_ZERO? Hi, On Mon, Jan 3, 2011 at 8:48 AM, Theodore Ts'o <tytso@....edu> 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@...il.com> 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@...il.com> 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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