Re: [PATCH v6 1/3] mm: add new api to enable ksm per process

[Stefan Roesch <shr@devkernel.io>]

David Hildenbrand <david@redhat.com> writes:

> On 12.04.23 20:41, David Hildenbrand wrote:
>> [...]
>>> That will work.
>>>> work? IOW, not exporting ksm_add_mm() and not passing a flag to __ksm_enter() --
>>>> it would simply set MMF_VM_MERGEABLE ?
>>>>
>>>
>>> ksm_add_mm() is also used in prctl (kernel/sys.c). Do you want to make a
>>> similar change there?
>> Yes.
>>
>>>>> + *
>>>>> + * @vma:  Pointer to vma
>>>>> + */
>>>>> +void ksm_add_vma(struct vm_area_struct *vma)
>>>>> +{
>>>>> +	struct mm_struct *mm = vma->vm_mm;
>>>>> +
>>>>> +	if (test_bit(MMF_VM_MERGE_ANY, &mm->flags))
>>>>> +		__ksm_add_vma(vma);
>>>>> +}
>>>>> +
>>>>> +/**
>>>>> + * ksm_add_vmas - Mark all vma's of a process as mergeable
>>>>> + *
>>>>> + * @mm:  Pointer to mm
>>>>> + */
>>>>> +void ksm_add_vmas(struct mm_struct *mm)
>>>>
>>>> I'd suggest calling this
>>>>
>>> I guess you forgot your name suggestion?
>> Yeah, I reconsidered because the first idea I had was not particularly
>> good. Maybe
>> ksm_enable_for_all_vmas()
>> But not so sure. If you think the "add" terminology is a good fit, keep
>> it like that.
>> Thanks for bearing with me :)
>>
>
> I briefly played with your patch to see how much it can be simplified.
> Always enabling ksm (setting MMF_VM_MERGEABLE) before setting
> MMF_VM_MERGE_ANY might simplify things. ksm_enable_merge_any() [or however it should
> be called] and ksm_fork() contain the interesting bits.
>
>
> Feel free to incorporate what you consider valuable (uncompiled,
> untested).
>
I added most of it. The only change is that I kept ksm_add_vmas as a
static function, otherwise I need to define the VMA_ITERATOR at the top
of the function.

>
> diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
> index 5a716bdcba05..5b2eef31398e 100644
> --- a/arch/s390/mm/gmap.c
> +++ b/arch/s390/mm/gmap.c
> @@ -2591,6 +2591,12 @@ int gmap_mark_unmergeable(void)
>  	int ret;
>  	VMA_ITERATOR(vmi, mm, 0);
>  +	/*
> +	 * Make sure to disable KSM (if enabled for the whole process or
> +	 * individual VMAs). Note that nothing currently hinders user space
> +	 * from re-enabling it.
> +	 */
> +	clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
>  	for_each_vma(vmi, vma) {
>  		/* Copy vm_flags to avoid partial modifications in ksm_madvise */
>  		vm_flags = vma->vm_flags;
> diff --git a/include/linux/ksm.h b/include/linux/ksm.h
> index 7e232ba59b86..c638b034d586 100644
> --- a/include/linux/ksm.h
> +++ b/include/linux/ksm.h
> @@ -18,13 +18,24 @@
>  #ifdef CONFIG_KSM
>  int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
>  		unsigned long end, int advice, unsigned long *vm_flags);
> +
> +void ksm_add_vma(struct vm_area_struct *vma);
> +int ksm_enable_merge_any(struct mm_struct *mm);
> +
>  int __ksm_enter(struct mm_struct *mm);
>  void __ksm_exit(struct mm_struct *mm);
>    static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
>  {
> -	if (test_bit(MMF_VM_MERGEABLE, &oldmm->flags))
> -		return __ksm_enter(mm);
> +	int ret;
> +
> +	if (test_bit(MMF_VM_MERGEABLE, &oldmm->flags)) {
> +		ret = __ksm_enter(mm);
> +		if (ret)
> +			return ret;
> +	}
> +	if (test_bit(MMF_VM_MERGE_ANY, &oldmm->flags))
> +		set_bit(MMF_VM_MERGE_ANY, &mm->flags);
>  	return 0;
>  }
>  @@ -53,6 +64,10 @@ void folio_migrate_ksm(struct folio *newfolio, struct folio
> *folio);
>    #else  /* !CONFIG_KSM */
>  +static inline void ksm_add_vma(struct vm_area_struct *vma)
> +{
> +}
> +
>  static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
>  {
>  	return 0;
> diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h
> index 0e17ae7fbfd3..0ee96ea7a0e9 100644
> --- a/include/linux/sched/coredump.h
> +++ b/include/linux/sched/coredump.h
> @@ -90,4 +90,5 @@ static inline int get_dumpable(struct mm_struct *mm)
>  #define MMF_INIT_MASK		(MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK |\
>  				 MMF_DISABLE_THP_MASK | MMF_HAS_MDWE_MASK)
>  +#define MMF_VM_MERGE_ANY	29
>  #endif /* _LINUX_SCHED_COREDUMP_H */
> diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
> index 1312a137f7fb..759b3f53e53f 100644
> --- a/include/uapi/linux/prctl.h
> +++ b/include/uapi/linux/prctl.h
> @@ -290,4 +290,6 @@ struct prctl_mm_map {
>  #define PR_SET_VMA		0x53564d41
>  # define PR_SET_VMA_ANON_NAME		0
>  +#define PR_SET_MEMORY_MERGE		67
> +#define PR_GET_MEMORY_MERGE		68
>  #endif /* _LINUX_PRCTL_H */
> diff --git a/kernel/sys.c b/kernel/sys.c
> index 495cd87d9bf4..8c2e50edeb18 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -15,6 +15,7 @@
>  #include <linux/highuid.h>
>  #include <linux/fs.h>
>  #include <linux/kmod.h>
> +#include <linux/ksm.h>
>  #include <linux/perf_event.h>
>  #include <linux/resource.h>
>  #include <linux/kernel.h>
> @@ -2661,6 +2662,30 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
>  	case PR_SET_VMA:
>  		error = prctl_set_vma(arg2, arg3, arg4, arg5);
>  		break;
> +#ifdef CONFIG_KSM
> +	case PR_SET_MEMORY_MERGE:
> +		if (mmap_write_lock_killable(me->mm))
> +			return -EINTR;
> +
> +		if (arg2) {
> +			error = ksm_enable_merge_any(me->mm);
> +		} else {
> +			/*
> +			 * TODO: we might want disable KSM on all VMAs and
> +			 * trigger unsharing to completely disable KSM.
> +			 */
> +			clear_bit(MMF_VM_MERGE_ANY, &me->mm->flags);
> +			error = 0;
> +		}
> +		mmap_write_unlock(me->mm);
> +		break;
> +	case PR_GET_MEMORY_MERGE:
> +		if (arg2 || arg3 || arg4 || arg5)
> +			return -EINVAL;
> +
> +		error = !!test_bit(MMF_VM_MERGE_ANY, &me->mm->flags);
> +		break;
> +#endif
>  	default:
>  		error = -EINVAL;
>  		break;
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 2b8d30068cbb..76ceec35395c 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -512,6 +512,28 @@ static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
>  	return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
>  }
>  +static bool vma_ksm_compatible(struct vm_area_struct *vma)
> +{
> +	if (vma->vm_flags & (VM_SHARED  | VM_MAYSHARE   | VM_PFNMAP  |
> +			     VM_IO      | VM_DONTEXPAND | VM_HUGETLB |
> +			     VM_MIXEDMAP))
> +		return false;		/* just ignore the advice */
> +
> +	if (vma_is_dax(vma))
> +		return false;
> +
> +#ifdef VM_SAO
> +	if (vma->vm_flags & VM_SAO)
> +		return false;
> +#endif
> +#ifdef VM_SPARC_ADI
> +	if (vma->vm_flags & VM_SPARC_ADI)
> +		return false;
> +#endif
> +
> +	return true;
> +}
> +
>  static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
>  		unsigned long addr)
>  {
> @@ -1020,6 +1042,7 @@ static int unmerge_and_remove_all_rmap_items(void)
>    			mm_slot_free(mm_slot_cache, mm_slot);
>  			clear_bit(MMF_VM_MERGEABLE, &mm->flags);
> +			clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
>  			mmdrop(mm);
>  		} else
>  			spin_unlock(&ksm_mmlist_lock);
> @@ -2395,6 +2418,7 @@ static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page)
>    		mm_slot_free(mm_slot_cache, mm_slot);
>  		clear_bit(MMF_VM_MERGEABLE, &mm->flags);
> +		clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
>  		mmap_read_unlock(mm);
>  		mmdrop(mm);
>  	} else {
> @@ -2471,6 +2495,52 @@ static int ksm_scan_thread(void *nothing)
>  	return 0;
>  }
>  +static void __ksm_add_vma(struct vm_area_struct *vma)
> +{
> +	unsigned long vm_flags = vma->vm_flags;
> +
> +	if (vm_flags & VM_MERGEABLE)
> +		return;
> +
> +	if (vma_ksm_compatible(vma)) {
> +		vm_flags |= VM_MERGEABLE;
> +		vm_flags_reset(vma, vm_flags);
> +	}
> +}
> +
> +/**
> + * ksm_add_vma - Mark vma as mergeable
> + *
> + * @vma:  Pointer to vma
> + */
> +void ksm_add_vma(struct vm_area_struct *vma)
> +{
> +	struct mm_struct *mm = vma->vm_mm;
> +
> +	if (test_bit(MMF_VM_MERGE_ANY, &mm->flags))
> +		__ksm_add_vma(vma);
> +}
> +
> +int ksm_enable_merge_any(struct mm_struct *mm)
> +{
> +	struct vm_area_struct *vma;
> +	int ret;
> +
> +	if (test_bit(MMF_VM_MERGE_ANY, mm->flags))
> +		return 0;
> +
> +	if (!test_bit(MMF_VM_MERGEABLE, mm->flags)) {
> +		ret = __ksm_enter(mm);
> +		if (ret)
> +			return ret;
> +	}
> +	set_bit(MMF_VM_MERGE_ANY, &mm->flags);
> +
> +	VMA_ITERATOR(vmi, mm, 0);
> +	for_each_vma(vmi, vma)
> +		__ksm_add_vma(vma);
> +}
> +
>  int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
>  		unsigned long end, int advice, unsigned long *vm_flags)
>  {
> @@ -2479,25 +2549,10 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
>    	switch (advice) {
>  	case MADV_MERGEABLE:
> -		/*
> -		 * Be somewhat over-protective for now!
> -		 */
> -		if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
> -				 VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
> -				 VM_HUGETLB | VM_MIXEDMAP))
> -			return 0;		/* just ignore the advice */
> -
> -		if (vma_is_dax(vma))
> +		if (vma->vm_flags & VM_MERGEABLE)
>  			return 0;
> -
> -#ifdef VM_SAO
> -		if (*vm_flags & VM_SAO)
> -			return 0;
> -#endif
> -#ifdef VM_SPARC_ADI
> -		if (*vm_flags & VM_SPARC_ADI)
> +		if (!vma_ksm_compatible(vma))
>  			return 0;
> -#endif
>    		if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
>  			err = __ksm_enter(mm);
> @@ -2601,6 +2656,7 @@ void __ksm_exit(struct mm_struct *mm)
>  	if (easy_to_free) {
>  		mm_slot_free(mm_slot_cache, mm_slot);
>  		clear_bit(MMF_VM_MERGEABLE, &mm->flags);
> +		clear_bit(MMF_VM_MERGE_ANY, &mm->flags);
>  		mmdrop(mm);
>  	} else if (mm_slot) {
>  		mmap_write_lock(mm);
> diff --git a/mm/mmap.c b/mm/mmap.c
> index ff68a67a2a7c..1f8619ff58ca 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -46,6 +46,7 @@
>  #include <linux/pkeys.h>
>  #include <linux/oom.h>
>  #include <linux/sched/mm.h>
> +#include <linux/ksm.h>
>    #include <linux/uaccess.h>
>  #include <asm/cacheflush.h>
> @@ -2659,6 +2660,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
>  	if (file && vm_flags & VM_SHARED)
>  		mapping_unmap_writable(file->f_mapping);
>  	file = vma->vm_file;
> +	ksm_add_vma(vma);
>  expanded:
>  	perf_event_mmap(vma);
>  @@ -2931,6 +2933,7 @@ static int do_brk_flags(struct vma_iterator *vmi, struct
> vm_area_struct *vma,
>  		goto mas_store_fail;
>    	mm->map_count++;
> +	ksm_add_vma(vma);
>  out:
>  	perf_event_mmap(vma);
>  	mm->total_vm += len >> PAGE_SHIFT;
> --
> 2.39.2