lkml.org 
[lkml]   [2020]   [Dec]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH v8 03/12] mm/bootmem_info: Introduce free_bootmem_page helper
    On Thu, Dec 10, 2020 at 11:55:17AM +0800, Muchun Song wrote:
    > Any memory allocated via the memblock allocator and not via the buddy
    > will be makred reserved already in the memmap. For those pages, we can
    marked
    > call free_bootmem_page() to free it to buddy allocator.
    >
    > Becasue we wan to free some vmemmap pages of the HugeTLB to the buddy
    Because want
    > allocator, we can use this helper to do that in the later patchs.
    patches

    To be honest, I think if would be best to introduce this along with
    patch#4, so we get to see where it gets used.

    > Signed-off-by: Muchun Song <songmuchun@bytedance.com>
    > ---
    > include/linux/bootmem_info.h | 19 +++++++++++++++++++
    > 1 file changed, 19 insertions(+)
    >
    > diff --git a/include/linux/bootmem_info.h b/include/linux/bootmem_info.h
    > index 4ed6dee1adc9..20a8b0df0c39 100644
    > --- a/include/linux/bootmem_info.h
    > +++ b/include/linux/bootmem_info.h
    > @@ -3,6 +3,7 @@
    > #define __LINUX_BOOTMEM_INFO_H
    >
    > #include <linux/mmzone.h>
    > +#include <linux/mm.h>

    <linux/mm.h> already includes <linux/mmzone.h>

    > +static inline void free_bootmem_page(struct page *page)
    > +{
    > + unsigned long magic = (unsigned long)page->freelist;
    > +
    > + /* bootmem page has reserved flag in the reserve_bootmem_region */
    reserve_bootmem_region sets the reserved flag on bootmem pages?

    > + VM_WARN_ON(!PageReserved(page) || page_ref_count(page) != 2);

    We do check for PageReserved in patch#4 before calling in here.
    Do we need yet another check here? IOW, do we need to be this paranoid?

    > + if (magic == SECTION_INFO || magic == MIX_SECTION_INFO)
    > + put_page_bootmem(page);
    > + else
    > + WARN_ON(1);

    Lately, some people have been complaining about using WARN_ON as some
    systems come with panic_on_warn set.

    I would say that in this case it does not matter much as if the vmemmap
    pages are not either SECTION_INFO or MIX_SECTION_INFO it means that a
    larger corruption happened elsewhere.

    But I think I would align the checks here.
    It does not make sense to me to only scream under DEBUG_VM if page's
    refcount differs from 2, and have a WARN_ON if the page we are trying
    to free was not used for the memmap array.
    Both things imply a corruption, so I would set the checks under the same
    configurations.

    --
    Oscar Salvador
    SUSE L3

    \
     
     \ /
      Last update: 2020-12-10 15:20    [W:3.580 / U:0.036 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site