David Hildenbrand <david@xxxxxxxxxx> 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
