forked from torvalds/linux
-
Notifications
You must be signed in to change notification settings - Fork 0
Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
mm, sparsemem: break out of loops early
There are a number of times that we loop over NR_MEM_SECTIONS, looking for section_present() on each section. But, when we have very large physical address spaces (large MAX_PHYSMEM_BITS), NR_MEM_SECTIONS becomes very large, making the loops quite long. With MAX_PHYSMEM_BITS=46 and a section size of 128MB, the current loops are 512k iterations, which we barely notice on modern hardware. But, raising MAX_PHYSMEM_BITS higher (like we will see on systems that support 5-level paging) makes this 64x longer and we start to notice, especially on slower systems like simulators. A 10-second delay for 512k iterations is annoying. But, a 640- second delay is crippling. This does not help if we have extremely sparse physical address spaces, but those are quite rare. We expect that most of the "slow" systems where this matters will also be quite small and non-sparse. To fix this, we track the highest section we've ever encountered. This lets us know when we will *never* see another section_present(), and lets us break out of the loops earlier. Doing the whole for_each_present_section_nr() macro is probably overkill, but it will ensure that any future loop iterations that we grow are more likely to be correct. Kirrill said "It shaved almost 40 seconds from boot time in qemu with 5-level paging enabled for me". Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Dave Hansen <[email protected]> Tested-by: Kirill A. Shutemov <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
- Loading branch information
Showing
3 changed files
with
52 additions
and
14 deletions.
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters