Re: [PATCH 7.2 v10 0/2] skip redundant sync IPIs when TLB flush sent them

Pasha Tatashin
2026-04-24T13:37:07Z

On 04-24 06:30, Andrew Morton wrote:
> On Fri, 24 Apr 2026 14:25:26 +0800 Lance Yang <lance.yang@linux.dev> wrote:
>
> > When page table operations require synchronization with software/lockless
> > walkers, they call tlb_remove_table_sync_{one,rcu}() after flushing the
> > TLB (tlb->freed_tables or tlb->unshared_tables).
> >
> > On architectures where the TLB flush already sends IPIs to all target CPUs,
> > the subsequent sync IPI broadcast is redundant. This is not only costly on
> > large systems where it disrupts all CPUs even for single-process page table
> > operations, but has also been reported to hurt RT workloads[1].
> >
> > This series introduces tlb_table_flush_implies_ipi_broadcast() to check if
> > the prior TLB flush already provided the necessary synchronization. When
> > true, the sync calls can early-return.
> >
> > A few cases rely on this synchronization:
> >
> > 1) hugetlb PMD unshare[2]: The problem is not the freeing but the reuse
> > of the PMD table for other purposes in the last remaining user after
> > unsharing.
> >
> > 2) khugepaged collapse[3]: Ensure no concurrent GUP-fast before collapsing
> > and (possibly) freeing the page table / re-depositing it.
>
> Sashiko questions:
> https://sashiko.dev/#/patchset/20260424062528.71951-1-lance.yang@linux.dev
>
> (I never know if my Sashiko emails are welcome/useful. Maybe Sashiko
> said the same stuff about v9 and it's all wrong. But better safe than
> sorry!)

These emails are helpful; but, I do not believe you should have to
manually follow up with a link to every new patch series.

Perhaps Sashiko could automatically send a summary email in response to
the cover letter, or provide a link once the reviews are complete. For
the kexec ML, we opted-in with Roman to receive automated emails from
sashiko.

+Cc: Roman.

>
>