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.
> And also check if section is present earlier. Then don't bother to
> allocate usemap and memmap if yes.
Moving the check up makes some sense.
> Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
The patch is not incorrect but I am wondering whether it is really worth
it for the current code base. Is it fixing anything real or it is a mere
code shuffling to please an eye?
> ---
> v1->v2:
> Do section existence checking earlier to further optimize code.
>
> mm/sparse.c | 29 +++++++++++------------------
> 1 file changed, 11 insertions(+), 18 deletions(-)
>
> diff --git a/mm/sparse.c b/mm/sparse.c
> index b2111f996aa6..f4f34d69131e 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -714,20 +714,18 @@ 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;
> - memmap = kmalloc_section_memmap(section_nr, nid, altmap);
> - if (!memmap)
> - return -ENOMEM;
> - usemap = __kmalloc_section_usemap();
> - if (!usemap) {
> - __kfree_section_memmap(memmap, altmap);
> - return -ENOMEM;
> - }
>
> ms = __pfn_to_section(start_pfn);
> - if (ms->section_mem_map & SECTION_MARKED_PRESENT) {
> - ret = -EEXIST;
> - goto out;
> + if (ms->section_mem_map & SECTION_MARKED_PRESENT)
> + return -EEXIST;
> +
> + usemap = __kmalloc_section_usemap();
> + if (!usemap)
> + return -ENOMEM;
> + memmap = kmalloc_section_memmap(section_nr, nid, altmap);
> + if (!memmap) {
> + kfree(usemap);
> + return -ENOMEM;
> }
>
> /*
> @@ -739,12 +737,7 @@ 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
>
--
Michal Hocko
SUSE Labs
