On Thu, Oct 1, 2020 at 8:27 AM Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> wrote: > > On Wed, Sep 30, 2020 at 03:42:17PM -0700, Lokesh Gidra wrote: > > On Wed, Sep 30, 2020 at 3:32 PM Kirill A. Shutemov > > <kirill.shutemov@xxxxxxxxxxxxxxx> wrote: > > > > > > On Wed, Sep 30, 2020 at 10:21:17PM +0000, Kalesh Singh wrote: > > > > mremap time can be optimized by moving entries at the PMD/PUD level if > > > > the source and destination addresses are PMD/PUD-aligned and > > > > PMD/PUD-sized. Enable moving at the PMD and PUD levels on arm64 and > > > > x86. Other architectures where this type of move is supported and known to > > > > be safe can also opt-in to these optimizations by enabling HAVE_MOVE_PMD > > > > and HAVE_MOVE_PUD. > > > > > > > > Observed Performance Improvements for remapping a PUD-aligned 1GB-sized > > > > region on x86 and arm64: > > > > > > > > - HAVE_MOVE_PMD is already enabled on x86 : N/A > > > > - Enabling HAVE_MOVE_PUD on x86 : ~13x speed up > > > > > > > > - Enabling HAVE_MOVE_PMD on arm64 : ~ 8x speed up > > > > - Enabling HAVE_MOVE_PUD on arm64 : ~19x speed up > > > > > > > > Altogether, HAVE_MOVE_PMD and HAVE_MOVE_PUD > > > > give a total of ~150x speed up on arm64. > > > > > > Is there a *real* workload that benefit from HAVE_MOVE_PUD? > > > > > We have a Java garbage collector under development which requires > > moving physical pages of multi-gigabyte heap using mremap. During this > > move, the application threads have to be paused for correctness. It is > > critical to keep this pause as short as possible to avoid jitters > > during user interaction. This is where HAVE_MOVE_PUD will greatly > > help. > > Any chance to quantify the effect of mremap() with and without > HAVE_MOVE_PUD? > > I doubt it's a major contributor to the GC pause. I expect you need to > move tens of gigs to get sizable effect. And if your GC routinely moves > tens of gigs, maybe problem somewhere else? > > I'm asking for numbers, because increase in complexity comes with cost. > If it doesn't provide an substantial benefit to a real workload > maintaining the code forever doesn't make sense. Lokesh on this thread would be better able to answer this. I'll let him weigh in here. Thanks, Kalesh > > -- > Kirill A. Shutemov > > -- > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@xxxxxxxxxxx. >
