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. >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
