linux-ext4 - Re: [PATCH RFC PKS/PMEM 33/58] fs/cramfs: Utilize new kmap

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Message-ID: <20201013205012.GI2046448@iweiny-DESK2.sc.intel.com>
Date:   Tue, 13 Oct 2020 13:50:12 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
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Subject: Re: [PATCH RFC PKS/PMEM 33/58] fs/cramfs: Utilize new kmap_thread()

On Tue, Oct 13, 2020 at 09:01:49PM +0100, Al Viro wrote:
> On Tue, Oct 13, 2020 at 08:36:43PM +0100, Matthew Wilcox wrote:
> 
> > static inline void copy_to_highpage(struct page *to, void *vfrom, unsigned int size)
> > {
> > 	char *vto = kmap_atomic(to);
> > 
> > 	memcpy(vto, vfrom, size);
> > 	kunmap_atomic(vto);
> > }
> > 
> > in linux/highmem.h ?
> 
> You mean, like
> static void memcpy_from_page(char *to, struct page *page, size_t offset, size_t len)
> {
>         char *from = kmap_atomic(page);
>         memcpy(to, from + offset, len);
>         kunmap_atomic(from);
> }
> 
> static void memcpy_to_page(struct page *page, size_t offset, const char *from, size_t len)
> {
>         char *to = kmap_atomic(page);
>         memcpy(to + offset, from, len);
>         kunmap_atomic(to);
> }
> 
> static void memzero_page(struct page *page, size_t offset, size_t len)
> {
>         char *addr = kmap_atomic(page);
>         memset(addr + offset, 0, len);
>         kunmap_atomic(addr);
> }
> 
> in lib/iov_iter.c?  FWIW, I don't like that "highpage" in the name and
> highmem.h as location - these make perfect sense regardless of highmem;
> they are normal memory operations with page + offset used instead of
> a pointer...

I was thinking along those lines as well especially because of the direction
this patch set takes kmap().

Thanks for pointing these out to me.  How about I lift them to a common header?
But if not highmem.h where?

Ira