Or use a PLB

By: Linus Torvalds (torvalds.delete@this.linux-foundation.org), September 25, 2021 11:21 am
Room: Moderated Discussions
sr (nobody.delete@this.nowhere.com) on September 25, 2021 12:07 pm wrote:
>
> And about memory allocation - for very small allocations fine granularity is acceptable but for
> larger ones isn't it wise to allocate to page limits even if hardware allows finer allocation?

Since the only reason to do this is for pointer checking, granularity of checking actually kind of matters.

And in many ways having a fixed granularity limit is ok - a lot of perfectly good algorithms do things like "over-read the end a string by one word to find the final NUL character" because they do vectorization (I mention the C string case, but that kind of thing happens in many other situations).

If you do pointer checking, you need to be able to deal with those kinds of benign pointer overruns.

That's fairly easy to do when you have a fixed allocation alignment checking limit.

But it's actually problematic if you sometimes get faults on a byte boundary, and sometimes at a page boundary. Then you effectively cannot use the optimistic version at all, or have to have some ridiculously complicated version.

It really sounds like you haven't actually ever used any of these kinds of things, and have never actually seen the problems they have in practice.

Linus
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TopicPosted ByDate
POWER10 SAP SD benchmarkanon22021/09/06 02:36 PM
  POWER10 SAP SD benchmarkDaniel B2021/09/07 01:31 AM
    "Cores" (and SPEC)Rayla2021/09/07 06:51 AM
      "Cores" (and SPEC)anon2021/09/07 02:56 PM
  POWER10 SAP SD benchmarkAnon2021/09/07 02:24 PM
    POWER10 SAP SD benchmarkAnon2021/09/07 02:27 PM
  Virtually tagged L1-cachessr2021/09/08 04:49 AM
    Virtually tagged L1-cachesdmcq2021/09/08 07:22 AM
      Virtually tagged L1-cachessr2021/09/08 07:56 AM
      Virtually tagged L1-cachesHugo Décharnes2021/09/08 07:58 AM
        Virtually tagged L1-cachessr2021/09/08 09:09 AM
          Virtually tagged L1-cachesHugo Décharnes2021/09/08 09:46 AM
            Virtually tagged L1-cachessr2021/09/08 10:35 AM
              Virtually tagged L1-cachesHugo Décharnes2021/09/08 11:23 AM
                Virtually tagged L1-cachessr2021/09/08 11:40 AM
                  Virtually tagged L1-cachesanon2021/09/09 02:16 AM
                    Virtually tagged L1-cachesKonrad Schwarz2021/09/10 04:19 AM
                      Virtually tagged L1-cachesHugo Décharnes2021/09/10 05:59 AM
                        Virtually tagged L1-cachesanon2021/09/14 02:17 AM
                          Virtually tagged L1-cachesdmcq2021/09/14 08:34 AM
                            Or use a PLB (NT)Paul A. Clayton2021/09/14 08:45 AM
                              Or use a PLBLinus Torvalds2021/09/14 02:27 PM
                                Or use a PLBanon2021/09/14 11:15 PM
                                  Or use a PLBMichael S2021/09/15 02:21 AM
                                    Or use a PLBdmcq2021/09/15 02:42 PM
                                      Or use a PLBKonrad Schwarz2021/09/16 03:24 AM
                                        Or use a PLBMichael S2021/09/16 09:13 AM
                                          Or use a PLB---2021/09/16 12:02 PM
                                  PLB referencePaul A. Clayton2021/09/18 01:35 PM
                                    PLB referenceMichael S2021/09/18 03:14 PM
                                      Demand paging/translation orthogonalPaul A. Clayton2021/09/19 06:33 AM
                                        Demand paging/translation orthogonalMichael S2021/09/19 08:10 AM
                                      PLB referenceCarson2021/09/20 09:19 PM
                                    PLB referencesr2021/09/20 05:02 AM
                                      PLB referenceMichael S2021/09/20 06:03 AM
                                        PLB referenceLinus Torvalds2021/09/20 11:10 AM
                                  Or use a PLBsr2021/09/20 03:32 AM
                              Or use a PLBsr2021/09/21 08:36 AM
                                Or use a PLBLinus Torvalds2021/09/21 09:04 AM
                                  Or use a PLBsr2021/09/21 09:48 AM
                                    Or use a PLBLinus Torvalds2021/09/21 12:55 PM
                                      Or use a PLBsr2021/09/22 05:55 AM
                                        Or use a PLBrwessel2021/09/22 06:09 AM
                                        Or use a PLBLinus Torvalds2021/09/22 10:50 AM
                                          Or use a PLBsr2021/09/22 12:00 PM
                                            Or use a PLBdmcq2021/09/22 03:07 PM
                                            Or use a PLBEtienne Lorrain2021/09/23 07:50 AM
                                          Or use a PLBanon22021/09/22 03:09 PM
                                            Or use a PLBdmcq2021/09/23 01:35 AM
                                          Or use a PLB2021/09/23 08:37 AM
                                            Or use a PLBLinus Torvalds2021/09/23 11:01 AM
                                              Or use a PLBgpd2021/09/24 02:59 AM
                                                Or use a PLBLinus Torvalds2021/09/24 09:45 AM
                                                  Or use a PLBdmcq2021/09/24 11:43 AM
                                                  Or use a PLBsr2021/09/25 09:19 AM
                                                    Or use a PLBLinus Torvalds2021/09/25 09:44 AM
                                                      Or use a PLBsr2021/09/25 10:11 AM
                                                        Or use a PLBLinus Torvalds2021/09/25 10:31 AM
                                                          Or use a PLBsr2021/09/25 10:52 AM
                                                            Or use a PLBLinus Torvalds2021/09/25 11:05 AM
                                                              Or use a PLBsr2021/09/25 11:23 AM
                                                                Or use a PLBrwessel2021/09/25 02:29 PM
                                                                  Or use a PLBsr2021/09/30 11:22 PM
                                                                    Or use a PLBrwessel2021/10/01 05:19 AM
                                                                      Or use a PLBDavid Hess2021/10/01 09:35 AM
                                                                        Or use a PLBrwessel2021/10/02 03:47 AM
                                                                      Or use a PLBsr2021/10/02 10:16 AM
                                                                        Or use a PLBrwessel2021/10/02 10:53 AM
                                                          Or use a PLBLinus Torvalds2021/09/25 10:57 AM
                                                            Or use a PLBsr2021/09/25 11:07 AM
                                                              Or use a PLBLinus Torvalds2021/09/25 11:21 AM
                                                                Or use a PLBsr2021/09/25 11:40 AM
                                                                  Or use a PLBnksingh2021/09/27 08:07 AM
                                                          Or use a PLB2021/09/27 08:02 AM
                                                            Or use a PLBLinus Torvalds2021/09/27 09:20 AM
                                                              Or use a PLBLinus Torvalds2021/09/27 11:58 AM
                                                                Or use a PLBdmcq2021/09/28 09:59 AM
                                              Or use a PLBsr2021/09/25 09:34 AM
                                                Or use a PLBrwessel2021/09/25 02:44 PM
                                                  Or use a PLBsr2021/10/01 12:04 AM
                                                    Or use a PLBrwessel2021/10/01 05:33 AM
                                                      I386 segmentation highlightssr2021/10/04 06:53 AM
                                                        I386 segmentation highlightsAdrian2021/10/04 08:53 AM
                                                          I386 segmentation highlightssr2021/10/04 09:19 AM
                                                        I386 segmentation highlightsrwessel2021/10/04 03:57 PM
                                                          I386 segmentation highlightssr2021/10/05 10:16 AM
                                                            I386 segmentation highlightsMichael S2021/10/05 11:27 AM
                                                            I386 segmentation highlightsrwessel2021/10/05 03:20 PM
                                                Or use a PLBJohnG2021/09/25 09:18 PM
                                              Or use a PLB2021/09/27 06:37 AM
                                                Or use a PLBHeikki Kultala2021/09/28 02:53 AM
                                                  Or use a PLBrwessel2021/09/28 06:29 AM
                                        Or use a PLBDavid Hess2021/09/23 05:00 PM
                                          Or use a PLBAdrian2021/09/24 12:21 AM
                                            Or use a PLBdmcq2021/09/25 11:41 AM
                                        Or use a PLBblaine2021/09/26 10:19 PM
                                          Or use a PLBDavid Hess2021/09/27 10:35 AM
                                            Or use a PLBblaine2021/09/27 04:19 PM
                                            Or use a PLBAdrian2021/09/27 09:40 PM
                                              Or use a PLBAdrian2021/09/27 09:59 PM
                                                Or use a PLBdmcq2021/09/28 06:45 AM
                                              Or use a PLBrwessel2021/09/28 06:45 AM
                                              Or use a PLBDavid Hess2021/09/28 11:50 AM
                                                Or use a PLBEtienne Lorrain2021/09/30 12:25 AM
                                                  Or use a PLBDavid Hess2021/10/01 09:40 AM
                                  MMU privilegessr2021/09/21 10:07 AM
                                    MMU privilegesLinus Torvalds2021/09/21 12:49 PM
                            Virtually tagged L1-cachesKonrad Schwarz2021/09/16 03:18 AM
                          Virtually tagged L1-cachesCarson2021/09/16 12:12 PM
                            Virtually tagged L1-cachesanon22021/09/16 04:16 PM
                              Virtually tagged L1-cachesrwessel2021/09/16 05:29 PM
                          Virtually tagged L1-cachessr2021/09/20 03:20 AM
              Virtually tagged L1-caches---2021/09/08 01:28 PM
                Virtually tagged L1-cachesanonymou52021/09/08 07:28 PM
                  Virtually tagged L1-cachesanonymou52021/09/08 07:34 PM
                  Virtually tagged L1-caches---2021/09/09 09:14 AM
                    Virtually tagged L1-cachesanonymou52021/09/09 09:44 PM
                Multi-threading?David Kanter2021/09/09 08:32 PM
                  Multi-threading?---2021/09/10 08:19 AM
                Virtually tagged L1-cachessr2021/09/11 12:19 AM
                Virtually tagged L1-cachessr2021/09/11 12:36 AM
                  Virtually tagged L1-caches---2021/09/11 08:53 AM
                    Virtually tagged L1-cachessr2021/09/11 11:43 PM
                      Virtually tagged L1-cachesLinus Torvalds2021/09/12 10:10 AM
                        Virtually tagged L1-cachessr2021/09/12 10:57 AM
                          Virtually tagged L1-cachesdmcq2021/09/13 07:31 AM
                            Virtually tagged L1-cachessr2021/09/20 03:11 AM
            Virtually tagged L1-cachessr2021/09/11 01:49 AM
      Virtually tagged L1-cachesLinus Torvalds2021/09/08 11:34 AM
        Virtually tagged L1-cachesdmcq2021/09/09 01:46 AM
          Virtually tagged L1-cachesdmcq2021/09/09 01:58 AM
          Virtually tagged L1-cachessr2021/09/11 12:29 AM
            Virtually tagged L1-cachesdmcq2021/09/11 07:59 AM
              Virtually tagged L1-cachessr2021/09/11 11:57 PM
                Virtually tagged L1-cachesdmcq2021/09/12 07:44 AM
                  Virtually tagged L1-cachessr2021/09/12 08:48 AM
                    Virtually tagged L1-cachesdmcq2021/09/12 12:22 PM
                      Virtually tagged L1-cachessr2021/09/20 03:40 AM
    Where do you see this information? (NT)anon22021/09/09 01:45 AM
      Where do you see this information?sr2021/09/11 12:40 AM
        Where do you see this information?anon22021/09/11 12:53 AM
          Where do you see this information?sr2021/09/11 01:08 AM
            Thank you (NT)anon22021/09/11 03:31 PM
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