On Sun, May 08, 2022 at 04:58:51PM +0800, Baolin Wang wrote:
> Hi,
>
> As Mike pointed out [1], the huge_ptep_get() will only return one specific
> pte value for the CONT-PTE or CONT-PMD size hugetlb on ARM64 system, which
> will not take into account the subpages' dirty or young bits of a CONT-PTE/PMD
> size hugetlb page. That will make us miss dirty or young flags of a CONT-PTE/PMD
> size hugetlb page for those functions that want to check the dirty or
> young flags of a hugetlb page. For example, the gather_hugetlb_stats() will
> get inaccurate dirty hugetlb page statistics, and the DAMON for hugetlb monitoring
> will also get inaccurate access statistics.
>
> To fix this issue, one approach is that we can define an ARM64 specific huge_ptep_get()
> implementation, which will take into account any subpages' dirty or young bits.
IIUC, we could get the page size by page_size(pte_page(pte)).
So, how about the following implementation of huge_ptep_get()?
Does this work for you?
pte_t huge_ptep_get(pte_t *ptep)
{
int ncontig, i;
size_t pgsize;
pte_t orig_pte = ptep_get(ptep);
if (!pte_present(orig_pte) || !pte_cont(orig_pte))
return orig_pte;
ncontig = num_contig_ptes(page_size(pte_page(orig_pte)), &pgsize);
for (i = 0; i < ncontig; i++, ptep++) {
pte_t pte = ptep_get(ptep);
if (pte_dirty(pte))
orig_pte = pte_mkdirty(orig_pte);
if (pte_young(pte))
orig_pte = pte_mkyoung(orig_pte);
}
return orig_pte;
}
> However we should add a new parameter for ARM64 specific huge_ptep_get() to check
> how many continuous PTEs or PMDs in this CONT-PTE/PMD size hugetlb, that means we
> should convert all the places using huge_ptep_get(), meanwhile most places using
> huge_ptep_get() did not care about the dirty or young flags at all.
>
> So instead of changing the prototype of huge_ptep_get(), this patch set introduces
> a new huge_ptep_get_access_flags() interface and define an ARM64 specific implementation,
> that will take into account any subpages' dirty or young bits for CONT-PTE/PMD size
> hugetlb page. And we can only change to use huge_ptep_get_access_flags() for those
> functions that care about the dirty or young flags of a hugetlb page.
>
> [1] https://lore.kernel.org/linux-mm/85bd80b4-b4fd-0d3f-a2e5-149559f2f387@xxxxxxxxxx/
>
> Baolin Wang (3):
> arm64/hugetlb: Introduce new huge_ptep_get_access_flags() interface
> fs/proc/task_mmu: Change to use huge_ptep_get_access_flags()
> mm/damon/vaddr: Change to use huge_ptep_get_access_flags()
>
> arch/arm64/include/asm/hugetlb.h | 2 ++
> arch/arm64/mm/hugetlbpage.c | 24 ++++++++++++++++++++++++
> fs/proc/task_mmu.c | 3 ++-
> include/asm-generic/hugetlb.h | 7 +++++++
> mm/damon/vaddr.c | 5 +++--
> 5 files changed, 38 insertions(+), 3 deletions(-)
>
> --
> 1.8.3.1
>
>
