Re: [PATCH v2 2/4] mm/sparse: Optimize sparse_add_one_section()

Mike Rapoport
2019-03-26T13:57:18Z

On Tue, Mar 26, 2019 at 09:45:22PM +0800, Baoquan He wrote:
> On 03/26/19 at 11:17am, Michal Hocko wrote:
> > On Tue 26-03-19 18:08:17, Baoquan He wrote:
> > > On 03/26/19 at 10:29am, Michal Hocko wrote:
> > > > On Tue 26-03-19 17:02:25, Baoquan He wrote:
> > > > > Reorder the allocation of usemap and memmap since usemap allocation
> > > > > is much simpler and easier. Otherwise hard work is done to make
> > > > > memmap ready, then have to rollback just because of usemap allocation
> > > > > failure.
> > > >
> > > > Is this really worth it? I can see that !VMEMMAP is doing memmap size
> > > > allocation which would be 2MB aka costly allocation but we do not do
> > > > __GFP_RETRY_MAYFAIL so the allocator backs off early.
> > >
> > > In !VMEMMAP case, it truly does simple allocation directly. surely
> > > usemap which size is 32 is smaller. So it doesn't matter that much who's
> > > ahead or who's behind. However, this benefit a little in VMEMMAP case.
> >
> > How does it help there? The failure should be even much less probable
> > there because we simply fall back to a small 4kB pages and those
> > essentially never fail.
>
> OK, I am fine to drop it. Or only put the section existence checking
> earlier to avoid unnecessary usemap/memmap allocation?
>
>
> From 7594b86ebf5d6fcc8146eca8fc5625f1961a15b1 Mon Sep 17 00:00:00 2001
> From: Baoquan He <bhe@redhat.com>
> Date: Tue, 26 Mar 2019 18:48:39 +0800
> Subject: [PATCH] mm/sparse: Check section's existence earlier in
> sparse_add_one_section()
>
> No need to allocate usemap and memmap if section has been present.
> And can clean up the handling on failure.
>
> Signed-off-by: Baoquan He <bhe@redhat.com>
> ---
> mm/sparse.c | 21 ++++++++-------------
> 1 file changed, 8 insertions(+), 13 deletions(-)
>
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 363f9d31b511..f564b531e0f7 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -714,7 +714,13 @@ int __meminit sparse_add_one_section(int nid, unsigned long start_pfn,
> ret = sparse_index_init(section_nr, nid);
> if (ret < 0 && ret != -EEXIST)
> return ret;
> - ret = 0;
> +
> + ms = __pfn_to_section(start_pfn);
> + if (ms->section_mem_map & SECTION_MARKED_PRESENT) {
> + ret = -EEXIST;
> + goto out;

return -EEXIST; ?

> + }
> +
> memmap = kmalloc_section_memmap(section_nr, nid, altmap);
> if (!memmap)
> return -ENOMEM;
> @@ -724,12 +730,6 @@ int __meminit sparse_add_one_section(int nid, unsigned long start_pfn,
> return -ENOMEM;
> }
>
> - ms = __pfn_to_section(start_pfn);
> - if (ms->section_mem_map & SECTION_MARKED_PRESENT) {
> - ret = -EEXIST;
> - goto out;
> - }
> -
> /*
> * Poison uninitialized struct pages in order to catch invalid flags
> * combinations.
> @@ -739,12 +739,7 @@ int __meminit sparse_add_one_section(int nid, unsigned long start_pfn,
> section_mark_present(ms);
> sparse_init_one_section(ms, section_nr, memmap, usemap);
>
> -out:
> - if (ret < 0) {
> - kfree(usemap);
> - __kfree_section_memmap(memmap, altmap);
> - }
> - return ret;
> + return 0;
> }
>
> #ifdef CONFIG_MEMORY_HOTREMOVE
> --
> 2.17.2
>

--
Sincerely yours,
Mike.