On Tue, 2019-02-19 at 12:04 +0100, Borislav Petkov wrote:

On Mon, Jan 28, 2019 at 04:34:16PM -0800, Rick Edgecombe wrote:

quoted

For architectures with CONFIG_ARCH_HAS_SET_ALIAS, pages can be unmapped
briefly on the directmap, even when CONFIG_DEBUG_PAGEALLOC is not
configured. So this changes kernel_map_pages and kernel_page_present to be

s/this changes/change/

From Documentation/process/submitting-patches.rst:

 "Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
  instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
  to do frotz", as if you are giving orders to the codebase to change
  its behaviour."

Also, please end function names with parentheses.

Yes, gotcha.

quoted

defined when CONFIG_ARCH_HAS_SET_ALIAS is defined as well. It also changes
places (page_alloc.c) where those functions are assumed to only be
implemented when CONFIG_DEBUG_PAGEALLOC is defined.

The commit message doesn't need to say "what" you're doing - that should
be obvious from the diff below. It should rather say "why" you're doing
it.

Ok, sorry. I'll change this to be more concise.

quoted

So now when CONFIG_ARCH_HAS_SET_ALIAS=y, hibernate will handle not present
page when saving. Previously this was already done when

pages

quoted

CONFIG_DEBUG_PAGEALLOC was configured. It does not appear to have a big
hibernating performance impact.

Comment over safe_copy_page

Oh, yes you are right.

quoted

Before:
[    4.670938] PM: Wrote 171996 kbytes in 0.21 seconds (819.02 MB/s)

After:
[    4.504714] PM: Wrote 178932 kbytes in 0.22 seconds (813.32 MB/s)

IINM, that's like 1734 pages more. How am I to understand this number?

Code has called set_alias_nv_noflush() on them and safe_copy_page() now
maps them one by one to copy them to the hibernation image?

Thx.

These are from logs hibernate generates. The concern was that hibernate could be
slightly slower because of the checking of whether the pages are mapped. The
bandwidth number can be used to compare, 819.02->813.32 MB/s. Some randomness
must have resulted in different amounts of memory used between tests. I can just
remove the log lines and include the bandwidth numbers.

Thanks,

Rick