From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Rapoport Subject: Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Date: Thu, 1 Jun 2017 14:00:48 +0300 Message-ID: <20170601110048.GE30495@rapoport-lnx> References: <20170524142735.GF3063@rapoport-lnx> <20170530074408.GA7969@dhcp22.suse.cz> <20170530101921.GA25738@rapoport-lnx> <20170530103930.GB7969@dhcp22.suse.cz> <20170530140456.GA8412@redhat.com> <20170530143941.GK7969@dhcp22.suse.cz> <20170530145632.GL7969@dhcp22.suse.cz> <20170530160610.GC8412@redhat.com> <20170531082414.GB27783@dhcp22.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20170531082414.GB27783@dhcp22.suse.cz> Sender: linux-kernel-owner@vger.kernel.org To: Michal Hocko Cc: Vlastimil Babka , Andrea Arcangeli , "Kirill A. Shutemov" , Andrew Morton , Arnd Bergmann , "Kirill A. Shutemov" , Pavel Emelyanov , linux-mm , lkml , Linux API List-Id: linux-api@vger.kernel.org On Wed, May 31, 2017 at 10:24:14AM +0200, Michal Hocko wrote: > On Wed 31-05-17 08:30:08, Vlastimil Babka wrote: > > On 05/30/2017 06:06 PM, Andrea Arcangeli wrote: > > > > > > I'm not sure if it should be considered a bug, the prctl is intended > > > to use normally by wrappers so it looks optimal as implemented this > > > way: affecting future vmas only, which will all be created after > > > execve executed by the wrapper. > > > > > > What's the point of messing with the prctl so it mangles over the > > > wrapper process own vmas before exec? Messing with those vmas is pure > > > wasted CPUs for the wrapper use case which is what the prctl was > > > created for. > > > > > > Furthermore there would be the risk a program that uses the prctl not > > > as a wrapper and then calls the prctl to clear VM_NOHUGEPAGE from > > > def_flags assuming the current kABI. The program could assume those > > > vmas that were instantiated before disabling the prctl are still with > > > VM_NOHUGEPAGE set (they would not after the change you propose). > > > > > > Adding a scan of all vmas to PR_SET_THP_DISABLE to clear VM_NOHUGEPAGE > > > on existing vmas looks more complex too and less finegrined so > > > probably more complex for userland to manage > > > > I would expect the prctl wouldn't iterate all vma's, nor would it modify > > def_flags anymore. It would just set a flag somewhere in mm struct that > > would be considered in addition to the per-vma flags when deciding > > whether to use THP. > > Exactly. Something like the below (not even compile tested). I did a quick go with the patch, compiles just fine :) It worked for my simple examples, the THP is enabled/disabled as expected and the vma->vm_flags are indeed unaffected. > > We could consider whether MADV_HUGEPAGE should be > > able to override the prctl or not. > > This should be a master override to any per vma setting. Here you've introduced a change to the current behaviour. Consider the following sequence: { prctl(PR_SET_THP_DISABLE); address = mmap(...); madvise(address, len, MADV_HUGEPAGE); } Currently, for the vma that backs the address transparent_hugepage_enabled(vma) will return true, and after your patch it will return false. The new behaviour may be more correct, I just wanted to bring the change to attention. > --- > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > index a3762d49ba39..9da053ced864 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -92,6 +92,7 @@ extern bool is_vma_temporary_stack(struct vm_area_struct *vma); > (1< ((__vma)->vm_flags & VM_HUGEPAGE))) && \ > !((__vma)->vm_flags & VM_NOHUGEPAGE) && \ > + !test_bit(MMF_DISABLE_THP, &(__vma)->vm_mm->flags) && \ > !is_vma_temporary_stack(__vma)) > #define transparent_hugepage_use_zero_page() \ > (transparent_hugepage_flags & \ > diff --git a/include/linux/khugepaged.h b/include/linux/khugepaged.h > index 5d9a400af509..f0d7335336cd 100644 > --- a/include/linux/khugepaged.h > +++ b/include/linux/khugepaged.h > @@ -48,7 +48,8 @@ static inline int khugepaged_enter(struct vm_area_struct *vma, > if (!test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags)) > if ((khugepaged_always() || > (khugepaged_req_madv() && (vm_flags & VM_HUGEPAGE))) && > - !(vm_flags & VM_NOHUGEPAGE)) > + !(vm_flags & VM_NOHUGEPAGE) && > + !test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags)) > if (__khugepaged_enter(vma->vm_mm)) > return -ENOMEM; > return 0; > diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h > index 69eedcef8f03..2c07b244090a 100644 > --- a/include/linux/sched/coredump.h > +++ b/include/linux/sched/coredump.h > @@ -68,6 +68,7 @@ static inline int get_dumpable(struct mm_struct *mm) > #define MMF_OOM_SKIP 21 /* mm is of no interest for the OOM killer */ > #define MMF_UNSTABLE 22 /* mm is unstable for copy_from_user */ > #define MMF_HUGE_ZERO_PAGE 23 /* mm has ever used the global huge zero page */ > +#define MMF_DISABLE_THP 24 /* disable THP for all VMAs */ > > #define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK) > > diff --git a/kernel/sys.c b/kernel/sys.c > index 8a94b4eabcaa..e48f0636c7fd 100644 > --- a/kernel/sys.c > +++ b/kernel/sys.c > @@ -2266,7 +2266,7 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, > case PR_GET_THP_DISABLE: > if (arg2 || arg3 || arg4 || arg5) > return -EINVAL; > - error = !!(me->mm->def_flags & VM_NOHUGEPAGE); > + error = !!test_bit(MMF_DISABLE_THP, &me->mm->flags); > break; > case PR_SET_THP_DISABLE: > if (arg3 || arg4 || arg5) > @@ -2274,9 +2274,9 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, > if (down_write_killable(&me->mm->mmap_sem)) > return -EINTR; > if (arg2) > - me->mm->def_flags |= VM_NOHUGEPAGE; > + set_bit(MMF_DISABLE_THP, &me->mm->flags); > else > - me->mm->def_flags &= ~VM_NOHUGEPAGE; > + clear_bit(MMF_DISABLE_THP, &me->mm->flags); > up_write(&me->mm->mmap_sem); > break; > case PR_MPX_ENABLE_MANAGEMENT: > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index ce29e5cc7809..57e31f4752b3 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -818,7 +818,8 @@ khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node) > static bool hugepage_vma_check(struct vm_area_struct *vma) > { > if ((!(vma->vm_flags & VM_HUGEPAGE) && !khugepaged_always()) || > - (vma->vm_flags & VM_NOHUGEPAGE)) > + (vma->vm_flags & VM_NOHUGEPAGE) || > + test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags)) > return false; > if (shmem_file(vma->vm_file)) { > if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE)) > diff --git a/mm/shmem.c b/mm/shmem.c > index e67d6ba4e98e..27fe1bbf813b 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -1977,10 +1977,11 @@ static int shmem_fault(struct vm_fault *vmf) > } > > sgp = SGP_CACHE; > - if (vma->vm_flags & VM_HUGEPAGE) > - sgp = SGP_HUGE; > - else if (vma->vm_flags & VM_NOHUGEPAGE) > + > + if ((vma->vm_flags & VM_NOHUGEPAGE) || test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags)) > sgp = SGP_NOHUGE; > + else if (vma->vm_flags & VM_HUGEPAGE) > + sgp = SGP_HUGE; > > error = shmem_getpage_gfp(inode, vmf->pgoff, &vmf->page, sgp, > gfp, vma, vmf, &ret); > -- > Michal Hocko > SUSE Labs >