Re: [PATCH v4 1/1] mm/highmem: Remove deprecated kmap_atomic

From: Ira Weiny
Date: Fri Nov 05 2021 - 12:56:25 EST


On Fri, Nov 05, 2021 at 01:49:21PM +0000, Matthew Wilcox wrote:
> On Thu, Feb 11, 2021 at 03:56:25PM -0800, Andrew Morton wrote:
> > On Wed, 10 Feb 2021 16:33:07 -0800 Ira Weiny <ira.weiny@xxxxxxxxx> wrote:
> >
> > > > Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> > >
> > > This already has my signed off by so I'm not going to 'review'. With Prathu's
> > > testing information I hope this can land.
> > >
> > > Andrew did you see this patch?
> >
> > I did now ;)
> >
> > Tossed onto the post-rc1 pile, thanks,
>
> This patch seems to have slipped through the gaps for a couple of cycles
> now? I found a missed spot in it for CONFIG_HIGHMEM:
>
> diff --git a/mm/highmem.c b/mm/highmem.c
> index 471d9779a7f4..82d8c5ab6e8d 100644
> --- a/mm/highmem.c
> +++ b/mm/highmem.c
> @@ -382,7 +382,7 @@ void zero_user_segments(struct page *page, unsigned start1, unsigned end1,
> unsigned this_end = min_t(unsigned, end1, PAGE_SIZE);
>
> if (end1 > start1) {
> - kaddr = kmap_atomic(page + i);
> + kaddr = kmap_local(page + i);

kmap_local_page()

> memset(kaddr + start1, 0, this_end - start1);
> }
> end1 -= this_end;
> @@ -397,7 +397,7 @@ void zero_user_segments(struct page *page, unsigned start1, unsigned end1,
>
> if (end2 > start2) {
> if (!kaddr)
> - kaddr = kmap_atomic(page + i);
> + kaddr = kmap_local(page + i);

kmap_local_page()

I'm ok with this. I'm not sure if Prathu needed this or not.

Also I wonder if memset_page could be used? It would end up mapping the page
2x sometimes.

As an aside I think flush_dcache_page() needs to be in memset_page() for
completeness but I'm a bit afraid of adding it with the current controversy...
:-/

Anyway, why hasn't Brathu's patch[1] landed yet?

I just checked 5.15 and it is not there? I don't even see it in the 5.16
merge? Perhaps it is coming in this merge window? Andrew?

Ira

[1] https://lore.kernel.org/lkml/20210204073255.20769-2-prathu.baronia@xxxxxxxxxxx/

> memset(kaddr + start2, 0, this_end - start2);
> }
> end2 -= this_end;
> @@ -405,7 +405,7 @@ void zero_user_segments(struct page *page, unsigned start1, unsigned end1,
> }
>
> if (kaddr) {
> - kunmap_atomic(kaddr);
> + kunmap_local(kaddr);
> flush_dcache_page(page + i);
> }