On Wed, Oct 27, 2021 at 10:35 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > On Wed, Oct 27, 2021 at 09:08:21AM -0700, Suren Baghdasaryan wrote: > > Unconditional mmap_write_lock around free_pgtables in exit_mmap seems > > to me the most semantically correct way forward and the pushback is on > > the basis of regressing performance of the exit path. I would like to > > measure that regression to confirm this. I don't have access to a big > > machine but will ask someone in another Google team to try the test > > Michal wrote here > > https://lore.kernel.org/all/20170725142626.GJ26723@xxxxxxxxxxxxxx/ on > > a server with and without a custom patch. > > Sorry to hijack this, but could you ask that team to also test this > patch? I think there's probably a good-sized win here, but I have no > profiles to share at this point. I've only done light testing, and > it may have bugs. > > NB: I only did the exit() path here. fork() conversion is left as an > exercise for the reader^W^W Liam. To clarify, this patch does not change the mmap_write_lock portion of exit_mmap. Do you want to test it in isolation or with the locking changes in exit_mmap I mentioned? > > From 5f9daa14a5e58c86a73eccf59abe23d131004926 Mon Sep 17 00:00:00 2001 > From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx> > Date: Wed, 27 Oct 2021 13:28:35 -0400 > Subject: [PATCH] mm: Add vmavec > > The vmavec lets us allocate and free batches of VMAs instead of > one at a time. Should improve fork() and exit() performance. > > Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> > --- > include/linux/vmavec.h | 38 ++++++++++++++++++++++++++++++++++++++ > kernel/fork.c | 17 +++++++++++++++++ > mm/mmap.c | 30 ++++++++++++++++++++++-------- > 3 files changed, 77 insertions(+), 8 deletions(-) > create mode 100644 include/linux/vmavec.h > > diff --git a/include/linux/vmavec.h b/include/linux/vmavec.h > new file mode 100644 > index 000000000000..8a324e2e1258 > --- /dev/null > +++ b/include/linux/vmavec.h > @@ -0,0 +1,38 @@ > +/* > + * A vma vector is an array of vm_area_structs, with a counter. > + */ > + > +struct vm_area_struct; > + > +#define VMAVEC_SIZE 15 > + > +struct vmavec { > + unsigned char nr; > + void *vmas[VMAVEC_SIZE]; > +}; > + > +#define VMAVEC(name) struct vmavec name = { } > + > +static inline bool vmavec_full(struct vmavec *vmavec) > +{ > + return vmavec->nr == VMAVEC_SIZE; > +} > + > +static inline bool vmavec_empty(struct vmavec *vmavec) > +{ > + return vmavec->nr == 0; > +} > + > +static inline > +void vmavec_push(struct vmavec *vmavec, struct vm_area_struct *vma) > +{ > + vmavec->vmas[vmavec->nr++] = vma; > +} > + > +static inline struct vm_area_struct *vmavec_pop(struct vmavec *vmavec) > +{ > + return vmavec->vmas[--vmavec->nr]; > +} > + > +void vm_area_free_vec(struct vmavec *vmavec); > +void vm_area_alloc_vec(struct mm_struct *mm, struct vmavec *vmavec); > diff --git a/kernel/fork.c b/kernel/fork.c > index 38681ad44c76..ea7e8bd00be8 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -97,6 +97,7 @@ > #include <linux/scs.h> > #include <linux/io_uring.h> > #include <linux/bpf.h> > +#include <linux/vmavec.h> > > #include <asm/pgalloc.h> > #include <linux/uaccess.h> > @@ -375,6 +376,22 @@ void vm_area_free(struct vm_area_struct *vma) > kmem_cache_free(vm_area_cachep, vma); > } > > +void vm_area_alloc_vec(struct mm_struct *mm, struct vmavec *vmavec) > +{ > + int i; > + > + vmavec->nr = kmem_cache_alloc_bulk(vm_area_cachep, GFP_KERNEL, > + VMAVEC_SIZE, vmavec->vmas); > + for (i = 0; i < vmavec->nr; i++) > + vma_init(vmavec->vmas[i], mm); > +} > + > +void vm_area_free_vec(struct vmavec *vmavec) > +{ > + kmem_cache_free_bulk(vm_area_cachep, vmavec->nr, vmavec->vmas); > + vmavec->nr = 0; > +} > + > static void account_kernel_stack(struct task_struct *tsk, int account) > { > void *stack = task_stack_page(tsk); > diff --git a/mm/mmap.c b/mm/mmap.c > index 88dcc5c25225..bff4e94eec8c 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -47,6 +47,7 @@ > #include <linux/pkeys.h> > #include <linux/oom.h> > #include <linux/sched/mm.h> > +#include <linux/vmavec.h> > > #include <linux/uaccess.h> > #include <asm/cacheflush.h> > @@ -172,19 +173,24 @@ void unlink_file_vma(struct vm_area_struct *vma) > } > } > > -/* > - * Close a vm structure and free it, returning the next. > - */ > -static struct vm_area_struct *remove_vma(struct vm_area_struct *vma) > +static void __remove_vma(struct vm_area_struct *vma) > { > - struct vm_area_struct *next = vma->vm_next; > - > might_sleep(); > if (vma->vm_ops && vma->vm_ops->close) > vma->vm_ops->close(vma); > if (vma->vm_file) > fput(vma->vm_file); > mpol_put(vma_policy(vma)); > +} > + > +/* > + * Close a vm structure and free it, returning the next. > + */ > +static struct vm_area_struct *remove_vma(struct vm_area_struct *vma) > +{ > + struct vm_area_struct *next = vma->vm_next; > + > + __remove_vma(vma); > vm_area_free(vma); > return next; > } > @@ -3125,6 +3131,7 @@ void exit_mmap(struct mm_struct *mm) > { > struct mmu_gather tlb; > struct vm_area_struct *vma; > + VMAVEC(vmavec); > unsigned long nr_accounted = 0; > > /* mm's last user has gone, and its about to be pulled down */ > @@ -3179,9 +3186,16 @@ void exit_mmap(struct mm_struct *mm) > while (vma) { > if (vma->vm_flags & VM_ACCOUNT) > nr_accounted += vma_pages(vma); > - vma = remove_vma(vma); > - cond_resched(); > + __remove_vma(vma); > + vmavec_push(&vmavec, vma); > + vma = vma->vm_next; > + if (vmavec_full(&vmavec)) { > + vm_area_free_vec(&vmavec); > + cond_resched(); > + } > } > + if (!vmavec_empty(&vmavec)) > + vm_area_free_vec(&vmavec); > vm_unacct_memory(nr_accounted); > } > > -- > 2.33.0 >
