On Wed, Jun 27, 2012 at 08:12:56AM -0700, Dan Magenheimer wrote: > > From: Minchan Kim [mailto:minchan@xxxxxxxxxx] > > Subject: Re: [PATCH 3/3] x86: add local_tlb_flush_kernel_range() > > > > Hello, > > > > On 06/27/2012 03:14 PM, Alex Shi wrote: > > > > > On 06/27/2012 01:53 PM, Minchan Kim wrote: > > > > > >> On 06/26/2012 01:14 AM, Seth Jennings wrote: > > >> > > >>> This patch adds support for a local_tlb_flush_kernel_range() > > >>> function for the x86 arch. This function allows for CPU-local > > >>> TLB flushing, potentially using invlpg for single entry flushing, > > >>> using an arch independent function name. > > >>> > > >>> Signed-off-by: Seth Jennings <sjenning@xxxxxxxxxxxxxxxxxx> > > >> > > >> > > >> Anyway, we don't matter INVLPG_BREAK_EVEN_PAGES's optimization point is 8 or something. > > > > > > > > > Different CPU type has different balance point on the invlpg replacing > > > flush all. and some CPU never get benefit from invlpg, So, it's better > > > to use different value for different CPU, not a fixed > > > INVLPG_BREAK_EVEN_PAGES. > > > > I think it could be another patch as further step and someone who are > > very familiar with architecture could do better than. > > So I hope it could be merged if it doesn't have real big problem. > > > > Thanks for the comment, Alex. > > Just my opinion, but I have to agree with Alex. Hardcoding > behavior that is VERY processor-specific is a bad idea. TLBs should > only be messed with when absolutely necessary, not for the > convenience of defending an abstraction that is nice-to-have > but, in current OS kernel code, unnecessary. At least put a big fat comment in the patch saying: "This is based on research done by Alex, where ... This needs to be redone where it is automatically figured out based on the CPUID, but ." [include what Dan just said about breakeven point] > > IIUC, zsmalloc only cares that the breakeven point is greater > than two. An arch-specific choice of (A) two page flushes > vs (B) one all-TLB flush should be all that is necessary right > now. (And, per separate discussion, even this isn't really > necessary either.) > > If zsmalloc _ever_ gets extended to support items that might > span three or more pages, a more generic TLB flush-pages-vs-flush-all > approach may be warranted and, by then, may already exist in some > future kernel. Until then, IMHO, keep it simple. Comments are simple :-) -- 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>