Re: [PATCH 4/7] mm, pagemap: remove SLOB and SLQB from comments and documentation

Vlastimil Babka
2023-03-15T11:06:02Z

On 3/14/23 09:19, Hyeonggon Yoo wrote:
> On Fri, Mar 10, 2023 at 11:32:06AM +0100, Vlastimil Babka wrote:
>> SLOB has been removed and SLQB never merged, so remove their mentions
>> from comments and documentation of pagemap.
>>
>> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
>> ---
>> Documentation/admin-guide/mm/pagemap.rst | 6 +++---
>> fs/proc/page.c | 5 ++---
>> 2 files changed, 5 insertions(+), 6 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst
>> index b5f970dc91e7..bb4aa897a773 100644
>> --- a/Documentation/admin-guide/mm/pagemap.rst
>> +++ b/Documentation/admin-guide/mm/pagemap.rst
>> @@ -91,9 +91,9 @@ Short descriptions to the page flags
>> The page is being locked for exclusive access, e.g. by undergoing read/write
>> IO.
>> 7 - SLAB
>> - The page is managed by the SLAB/SLOB/SLUB/SLQB kernel memory allocator.
>> - When compound page is used, SLUB/SLQB will only set this flag on the head
>> - page; SLOB will not flag it at all.
>> + The page is managed by the SLAB/SLUB kernel memory allocator.
>> + When compound page is used, either will only set this flag on the head
>> + page..
>> 10 - BUDDY
>> A free memory block managed by the buddy system allocator.
>> The buddy system organizes free memory in blocks of various orders.
>> diff --git a/fs/proc/page.c b/fs/proc/page.c
>> index 6249c347809a..1356aeffd8dc 100644
>> --- a/fs/proc/page.c
>> +++ b/fs/proc/page.c
>> @@ -125,7 +125,7 @@ u64 stable_page_flags(struct page *page)
>> /*
>> * pseudo flags for the well known (anonymous) memory mapped pages
>> *
>> - * Note that page->_mapcount is overloaded in SLOB/SLUB/SLQB, so the
>> + * Note that page->_mapcount is overloaded in SLAB/SLUB, so the
>
> SLUB does not overload _mapcount.

True, I overlooked that, thanks.

>> * simple test in page_mapped() is not enough.
>> */
>> if (!PageSlab(page) && page_mapped(page))
>> @@ -166,8 +166,7 @@ u64 stable_page_flags(struct page *page)
>>
>> /*
>> * Caveats on high order pages: page->_refcount will only be set
>> - * -1 on the head page; SLUB/SLQB do the same for PG_slab;
>> - * SLOB won't set PG_slab at all on compound pages.
>> + * -1 on the head page; SLAB/SLUB do the same for PG_slab;
>
> I think this comment could be just saying that PG_buddy is only set on
> head page, not saying
>
> _refcount is set to -1 on head page (is it even correct?)

It's not, that scheme is outdated. So I'll have it mention PG_buddy as you
suggest, but PG_slab also needs special care as it's not set on tail pages.
But I noticed the compound_head() is unnecessary as that's covered by
PageSlab() which is defined as PF_NO_TAIL. So the sum of modifications to
this patch:

diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst
index bb4aa897a773..c8f380271cad 100644
--- a/Documentation/admin-guide/mm/pagemap.rst
+++ b/Documentation/admin-guide/mm/pagemap.rst
@@ -93,7 +93,7 @@ Short descriptions to the page flags
7 - SLAB
The page is managed by the SLAB/SLUB kernel memory allocator.
When compound page is used, either will only set this flag on the head
- page..
+ page.
10 - BUDDY
A free memory block managed by the buddy system allocator.
The buddy system organizes free memory in blocks of various orders.
diff --git a/fs/proc/page.c b/fs/proc/page.c
index 1356aeffd8dc..195b077c0fac 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -125,7 +125,7 @@ u64 stable_page_flags(struct page *page)
/*
* pseudo flags for the well known (anonymous) memory mapped pages
*
- * Note that page->_mapcount is overloaded in SLAB/SLUB, so the
+ * Note that page->_mapcount is overloaded in SLAB, so the
* simple test in page_mapped() is not enough.
*/
if (!PageSlab(page) && page_mapped(page))
@@ -165,8 +165,8 @@ u64 stable_page_flags(struct page *page)

/*
- * Caveats on high order pages: page->_refcount will only be set
- * -1 on the head page; SLAB/SLUB do the same for PG_slab;
+ * Caveats on high order pages: PG_buddy and PG_slab will only be set
+ * on the head page.
*/
if (PageBuddy(page))
u |= 1 << KPF_BUDDY;
@@ -184,7 +184,7 @@ u64 stable_page_flags(struct page *page)
u |= kpf_copy_bit(k, KPF_LOCKED, PG_locked);

u |= kpf_copy_bit(k, KPF_SLAB, PG_slab);
- if (PageTail(page) && PageSlab(compound_head(page)))
+ if (PageTail(page) && PageSlab(page))
u |= 1 << KPF_SLAB;

u |= kpf_copy_bit(k, KPF_ERROR, PG_error);