> From: Seth Jennings [mailto:sjenning@xxxxxxxxxxxxxxxxxx] > Sent: Friday, June 15, 2012 9:13 AM > To: Peter Zijlstra > Cc: Minchan Kim; Greg Kroah-Hartman; Nitin Gupta; Dan Magenheimer; linux-kernel@xxxxxxxxxxxxxxx; > linux-mm@xxxxxxxxx; Thomas Gleixner; Ingo Molnar; Tejun Heo; David Howells; x86@xxxxxxxxxx; Nick > Piggin > Subject: Re: [PATCH v2 3/3] x86: Support local_flush_tlb_kernel_range > > On 05/17/2012 09:51 AM, Peter Zijlstra wrote: > > > On Thu, 2012-05-17 at 17:11 +0900, Minchan Kim wrote: > >>> +++ b/arch/x86/include/asm/tlbflush.h > >>> @@ -172,4 +172,16 @@ static inline void flush_tlb_kernel_range(unsigned long start, > >>> flush_tlb_all(); > >>> } > >>> > >>> +static inline void local_flush_tlb_kernel_range(unsigned long start, > >>> + unsigned long end) > >>> +{ > >>> + if (cpu_has_invlpg) { > >>> + while (start < end) { > >>> + __flush_tlb_single(start); > >>> + start += PAGE_SIZE; > >>> + } > >>> + } else > >>> + local_flush_tlb(); > >>> +} > > > > It would be much better if you wait for Alex Shi's patch to mature. > > doing the invlpg thing for ranges is not an unconditional win. > > From what I can tell Alex's patches have stalled. The last post was v6 > on 5/17 and there wasn't a single reply to them afaict. > > According to Alex's investigation of this "tipping point", it seems that > a good generic value is 8. In other words, on most x86 hardware, it is > cheaper to flush up to 8 tlb entries one by one rather than doing a > complete flush. > > So we can do something like: > > if (cpu_has_invlpg && (end - start)/PAGE_SIZE <= 8) { > while (start < end) { > > Would this be acceptable? Hey Seth, Nitin -- After more work digging around zsmalloc and zbud, I really think this TLB flushing, as well as the "page pair mapping" code can be completely eliminated IFF zsmalloc is limited to items PAGE_SIZE or less. Since this is already true of zram (and in-tree zcache), and zsmalloc currently has no other users, I think you should seriously consider limiting zsmalloc in that way, or possibly splitting out one version of zsmalloc which handles items PAGE_SIZE or less, and a second version that can handle larger items but has (AFAIK) no users. If you consider it an option to have (a version of) zsmalloc limited to items PAGE_SIZE or less, let me know and we can get into the details. Thanks, Dan -- 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