Re: [PATCH v2] mm/damon/vaddr: attempt per-vma lock during page table walk

[Kefeng Wang <wangkefeng.wang@huawei.com>]

On 5/14/2026 10:00 AM, SeongJae Park wrote:
> On Tue, 12 May 2026 23:15:23 +0800 Kefeng Wang <wangkefeng.wang@huawei.com> wrote:
> 
>> Currently, DAMON virtual address operations use mmap_read_lock
>> during page table walks, which can cause unnecessary contention
>> under high concurrency.
>>
>> Introduce damon_va_walk_page_range() to first attempt acquiring a
>> per-vma lock. If the VMA is found and the range is fully contained
>> within it, the page table walk proceeds with the per-vma lock
>> instead of mmap_read_lock.
>>
>> This optimization is particularly effective for damon_va_young()
>> and damon_va_mkold(), which are frequently called and typically
>> operate within a single VMA.
> 
> Maybe this is not only making DAMON faster, but avoid DAMON blocking others.
> 
Yes, this is exactly what per-vma is for.


> And because we don't have performance measurements, how about making this
> sentence less assertive?  E.g., "This optimization is particularly expected to
> be effective for ..."

Fine to me.

> 
> I guess Andrew could make the adjustment when he picks this into mm.git.  If
> not I will repost this with the trivial change if you don't mind.
> 
>>

Sure

>> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> 
> Reviewed-by: SeongJae Park <sj@kernel.org>
> 

Thanks

>> ---
>> v2: avoid handling VMAs with the VM_PFNMAP for per-vma path, found by
>>      Sashiko review.
> 
> This patch helped Sashiko finding [1] yet another DAMON bug (impact is minor
> imho).  The bug is orthogonal to this patch so there is no blocker for this
> patch.
> 
>> v1: https://lore.kernel.org/linux-mm/20260511132546.1973270-1-wangkefeng.wang@huawei.com/
> 
> [1] https://lore.kernel.org/20260514015053.149396-1-sj@kernel.org
> 
> 
> Thanks,
> SJ
> 
> [...]
>