On Fri, Oct 12, 2018 at 05:42:24PM +0100, Anton Ivanov wrote: > > On 10/12/18 3:48 PM, Anton Ivanov wrote: > > On 12/10/2018 15:37, Kirill A. Shutemov wrote: > > > On Fri, Oct 12, 2018 at 03:09:49PM +0100, Anton Ivanov wrote: > > > > On 10/12/18 2:37 AM, Joel Fernandes (Google) wrote: > > > > > Android needs to mremap large regions of memory during > > > > > memory management > > > > > related operations. The mremap system call can be really > > > > > slow if THP is > > > > > not enabled. The bottleneck is move_page_tables, which is copying each > > > > > pte at a time, and can be really slow across a large map. > > > > > Turning on THP > > > > > may not be a viable option, and is not for us. This patch > > > > > speeds up the > > > > > performance for non-THP system by copying at the PMD level > > > > > when possible. > > > > > > > > > > The speed up is three orders of magnitude. On a 1GB mremap, the mremap > > > > > completion times drops from 160-250 millesconds to 380-400 > > > > > microseconds. > > > > > > > > > > Before: > > > > > Total mremap time for 1GB data: 242321014 nanoseconds. > > > > > Total mremap time for 1GB data: 196842467 nanoseconds. > > > > > Total mremap time for 1GB data: 167051162 nanoseconds. > > > > > > > > > > After: > > > > > Total mremap time for 1GB data: 385781 nanoseconds. > > > > > Total mremap time for 1GB data: 388959 nanoseconds. > > > > > Total mremap time for 1GB data: 402813 nanoseconds. > > > > > > > > > > Incase THP is enabled, the optimization is skipped. I also flush the > > > > > tlb every time we do this optimization since I couldn't find a way to > > > > > determine if the low-level PTEs are dirty. It is seen that the cost of > > > > > doing so is not much compared the improvement, on both > > > > > x86-64 and arm64. > > > > > > > > > > Cc: minc...@kernel.org > > > > > Cc: pan...@google.com > > > > > Cc: hu...@google.com > > > > > Cc: lokeshgi...@google.com > > > > > Cc: dan...@google.com > > > > > Cc: mho...@kernel.org > > > > > Cc: kir...@shutemov.name > > > > > Cc: a...@linux-foundation.org > > > > > Signed-off-by: Joel Fernandes (Google) <j...@joelfernandes.org> > > > > > --- > > > > > mm/mremap.c | 62 > > > > > +++++++++++++++++++++++++++++++++++++++++++++++++++++ > > > > > 1 file changed, 62 insertions(+) > > > > > > > > > > diff --git a/mm/mremap.c b/mm/mremap.c > > > > > index 9e68a02a52b1..d82c485822ef 100644 > > > > > --- a/mm/mremap.c > > > > > +++ b/mm/mremap.c > > > > > @@ -191,6 +191,54 @@ static void move_ptes(struct > > > > > vm_area_struct *vma, pmd_t *old_pmd, > > > > > drop_rmap_locks(vma); > > > > > } > > > > > +static bool move_normal_pmd(struct vm_area_struct *vma, > > > > > unsigned long old_addr, > > > > > + unsigned long new_addr, unsigned long old_end, > > > > > + pmd_t *old_pmd, pmd_t *new_pmd, bool *need_flush) > > > > > +{ > > > > > + spinlock_t *old_ptl, *new_ptl; > > > > > + struct mm_struct *mm = vma->vm_mm; > > > > > + > > > > > + if ((old_addr & ~PMD_MASK) || (new_addr & ~PMD_MASK) > > > > > + || old_end - old_addr < PMD_SIZE) > > > > > + return false; > > > > > + > > > > > + /* > > > > > + * The destination pmd shouldn't be established, free_pgtables() > > > > > + * should have release it. > > > > > + */ > > > > > + if (WARN_ON(!pmd_none(*new_pmd))) > > > > > + return false; > > > > > + > > > > > + /* > > > > > + * We don't have to worry about the ordering of src and dst > > > > > + * ptlocks because exclusive mmap_sem prevents deadlock. > > > > > + */ > > > > > + old_ptl = pmd_lock(vma->vm_mm, old_pmd); > > > > > + if (old_ptl) { > > > > > + pmd_t pmd; > > > > > + > > > > > + new_ptl = pmd_lockptr(mm, new_pmd); > > > > > + if (new_ptl != old_ptl) > > > > > + spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING); > > > > > + > > > > > + /* Clear the pmd */ > > > > > + pmd = *old_pmd; > > > > > + pmd_clear(old_pmd); > > > > > + > > > > > + VM_BUG_ON(!pmd_none(*new_pmd)); > > > > > + > > > > > + /* Set the new pmd */ > > > > > + set_pmd_at(mm, new_addr, new_pmd, pmd); > > > > UML does not have set_pmd_at at all > > > Every architecture does. :) > > > > I tried to build it patching vs 4.19-rc before I made this statement and > > ran into that. > > > > Presently it does not. > > > > https://elixir.bootlin.com/linux/v4.19-rc7/ident/set_pmd_at - UML is not > > on the list. > > Once this problem as well as the omissions in the include changes for UML in > patch one have been fixed it appears to be working. > > What it needs is attached. > > > > > > > > > > But it may come not from the arch code. > > > > There is no generic definition as far as I can see. All 12 defines in > > 4.19 are in arch specific code. Unless i am missing something... > > > > > > > > > If I read the code right, MIPS completely ignores the address > > > > argument so > > > > set_pmd_at there may not have the effect which this patch is trying to > > > > achieve. > > > Ignoring address is fine. Most architectures do that.. > > > The ideas is to move page table to the new pmd slot. It's nothing to do > > > with the address passed to set_pmd_at(). > > > > If that is it's only function, then I am going to appropriate the code > > out of the MIPS tree for further uml testing. It does exactly that - > > just move the pmd the new slot. > > > > > > > A. > > > A. >
> From ac265d96897a346b05646fce91784ed4922c7f8d Mon Sep 17 00:00:00 2001 > From: Anton Ivanov <anton.iva...@cambridgegreys.com> > Date: Fri, 12 Oct 2018 17:24:10 +0100 > Subject: [PATCH] Incremental fixes to the mmremap patch > > Signed-off-by: Anton Ivanov <anton.iva...@cambridgegreys.com> > --- > arch/um/include/asm/pgalloc.h | 4 ++-- > arch/um/include/asm/pgtable.h | 3 +++ > arch/um/kernel/tlb.c | 6 ++++++ > 3 files changed, 11 insertions(+), 2 deletions(-) > > diff --git a/arch/um/include/asm/pgalloc.h b/arch/um/include/asm/pgalloc.h > index bf90b2aa2002..99eb5682792a 100644 > --- a/arch/um/include/asm/pgalloc.h > +++ b/arch/um/include/asm/pgalloc.h > @@ -25,8 +25,8 @@ > extern pgd_t *pgd_alloc(struct mm_struct *); > extern void pgd_free(struct mm_struct *mm, pgd_t *pgd); > > -extern pte_t *pte_alloc_one_kernel(struct mm_struct *, unsigned long); > -extern pgtable_t pte_alloc_one(struct mm_struct *, unsigned long); > +extern pte_t *pte_alloc_one_kernel(struct mm_struct *); > +extern pgtable_t pte_alloc_one(struct mm_struct *); If its Ok, let me handle this bit since otherwise it complicates things for me. > static inline void pte_free_kernel(struct mm_struct *mm, pte_t *pte) > { > diff --git a/arch/um/include/asm/pgtable.h b/arch/um/include/asm/pgtable.h > index 7485398d0737..1692da55e63a 100644 > --- a/arch/um/include/asm/pgtable.h > +++ b/arch/um/include/asm/pgtable.h > @@ -359,4 +359,7 @@ do { \ > __flush_tlb_one((vaddr)); \ > } while (0) > > +extern void set_pmd_at(struct mm_struct *mm, unsigned long addr, > + pmd_t *pmdp, pmd_t pmd); > + > #endif > diff --git a/arch/um/kernel/tlb.c b/arch/um/kernel/tlb.c > index 763d35bdda01..d17b74184ba0 100644 > --- a/arch/um/kernel/tlb.c > +++ b/arch/um/kernel/tlb.c > @@ -647,3 +647,9 @@ void force_flush_all(void) > vma = vma->vm_next; > } > } > +void set_pmd_at(struct mm_struct *mm, unsigned long addr, > + pmd_t *pmdp, pmd_t pmd) > +{ > + *pmdp = pmd; > +} > + I believe this should be included in a separate patch since it is not related specifically to pte_alloc argument removal. If you want, I could split it into a separate patch for my series with you as author. thanks, - Joel