Re: Ack to merge through DRM? WAS Re: [PATCH v2 1/5] mm: Add write-protect and clean utilities for address space ranges
From: Thomas HellstrÃm (VMware)
Date: Mon Sep 30 2019 - 17:16:35 EST
On 9/30/19 7:12 PM, Linus Torvalds wrote:
On Mon, Sep 30, 2019 at 6:04 AM Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote:
Have you seen page_vma_mapped_walk()? I made it specifically for rmap code
to cover cases when a THP is mapped with PTEs. To me it's not a big
stretch to make it cover multiple pages too.
I agree that is closer, but it does make for calling that big complex
function for every iteration step.
Of course, you are right that the callback approach is problematic
too, now that we have retpoline issues, making those very expensive.
But at least that hopefully gets fixed some day and gets to be a rare
problem.
Matter ot taste, I guess.
Linus
Matthew Wilcox suggested something similar before the pagewalk.c rewrite:
https://lore.kernel.org/lkml/20190806190937.GD30179@xxxxxxxxxxxxxxxxxxxxxx/
Still, In this case I'd opt for using the pagewalk code: In the dirty
helpers we don't ever use a struct page, but only deal with PTE entries,
same as the pagewalk code does, but not page_vma_mapped_walk(). The
underlying memory may well be IO memory.
/Thomas