On 06/08/2018 03:57 PM, Andrew Morton wrote: > On Fri, 8 Jun 2018 14:56:52 -0400 Jason Baron <jbaron@xxxxxxxxxx> wrote: > >> In order to free memory that is marked MLOCK_ONFAULT, the memory region >> needs to be first unlocked, before calling MADV_DONTNEED. And if the region >> is to be reused as MLOCK_ONFAULT, we require another call to mlock2() with >> the MLOCK_ONFAULT flag. >> >> Let's simplify freeing memory that is set MLOCK_ONFAULT, by allowing >> MADV_DONTNEED to work directly for memory that is set MLOCK_ONFAULT. The >> locked memory limits, tracked by mm->locked_vm do not need to be adjusted >> in this case, since they were charged to the entire region when >> MLOCK_ONFAULT was initially set. > > Seems useful. > > Is a manpage update planned? > Yes, I will add a manpage update. I sort of wanted to see first if people thought this patch was a reasonable thing to do. > Various updates to tools/testing/selftests/vm/* seem appropriate. > Indeed, I started updating tootls/testing/selftests/vm/mlock2-tests.c with this new interface, but then I realized that that test is failing before I made any changes. So I will go back and sort that out, and add additional testing for this new interface. >> Further, I don't think allowing MADV_FREE for MLOCK_ONFAULT regions makes >> sense, since the point of MLOCK_ONFAULT is for userspace to know when pages >> are locked in memory and thus to know when page faults will occur. > > This sounds non-backward-compatible? > I was making the point of why I think allowing 'MADV_DONTNEED' for MLOCK_ONFAULT regions makes sense, while allowing 'MADV_FREE' for MLOCK_ONFAULT regions really does not. Thanks, -Jason
