On 12/10/21 16:29, Hyeonggon Yoo wrote:
> On Fri, Dec 10, 2021 at 12:44:32PM +0100, Vlastimil Babka wrote:
>> On 12/10/21 11:44, Hyeonggon Yoo wrote:
>> > On Wed, Dec 01, 2021 at 07:15:01PM +0100, Vlastimil Babka wrote:
>> >> From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
>> >>
>> >> Use struct slab throughout the slob allocator.
>> >>
>> >> [ vbabka@xxxxxxx: don't introduce wrappers for PageSlobFree in mm/slab.h just
>> >> for the single callers being wrappers in mm/slob.c ]
>> >>
>> >> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
>> >> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
>> >> ---
>> >> mm/slob.c | 34 +++++++++++++++++-----------------
>> >> 1 file changed, 17 insertions(+), 17 deletions(-)
>> >>
>> >> diff --git a/mm/slob.c b/mm/slob.c
>> >> index d2d15e7f191c..d3512bcc3141 100644
>> >> --- a/mm/slob.c
>> >> +++ b/mm/slob.c
>> >
>> > ...
>> >
>> >> /* Enough room on this page? */
>> >> @@ -358,8 +358,8 @@ static void *slob_alloc(size_t size, gfp_t gfp, int align, int node,
>> >> b = slob_new_pages(gfp & ~__GFP_ZERO, 0, node);
>> >> if (!b)
>> >> return NULL;
>> >> - sp = virt_to_page(b);
>> >> - __SetPageSlab(sp);
>> >> + sp = virt_to_slab(b);
>> >> + __SetPageSlab(slab_page(sp));
>> >
>> > Hello Vlastimil.
>> >
>> > I've tested this patch on my machine and it causes NULL pointer dereference.
>> > that's because virt_to_slab returns NULL if folio_test_slab is false.
>> > and __SetPageSlab is called with sp = NULL.
>>
>> Oops, thanks for catching this.
>>
>> > diff below fixed bug.
>>
>> Changed it to use folio and will push an updated branch
>> slab-struct_slab-v3r2
>>
>> Thanks!
>
> Tested again on slab-struct_slab-v3r2 and everyting works fine!
> And the code overall looks good to me.
>
> Reviewed-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
> Tested-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
Thanks!
> And below is not about this patch,
> but what about something like this?
>
> Because it's not necessary that page->_mapcount and
> slab->units have same offset, so we can remove
> (somewhat confusing) page_mapcount_reset function call.
Yeah this could be done as new patch on top of 21/33. I wouldn't squash it
there so that it remains just a split without functional change.
> I want to remove calling page_mapcount_reset also in
> SLAB, but I have no idea. (maybe we can do that if we remove
> SLAB colouring but that's going too far)
>
> diff --git a/mm/slab.h b/mm/slab.h
> index 90d7fceba470..dd0480149d38 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -50,8 +50,8 @@ struct slab {
> struct list_head slab_list;
> void * __unused_1;
> void *freelist; /* first free block */
> - void * __unused_2;
> - int units;
> + long units;
> + unsigned int __unused_2;
>
> #else
> #error "Unexpected slab allocator configured"
> diff --git a/mm/slob.c b/mm/slob.c
> index 39b651b3e6e7..7b2d2c7d69cc 100644
> --- a/mm/slob.c
> +++ b/mm/slob.c
> @@ -404,7 +404,6 @@ static void slob_free(void *block, int size)
> clear_slob_page_free(sp);
> spin_unlock_irqrestore(&slob_lock, flags);
> __ClearPageSlab(slab_page(sp));
> - page_mapcount_reset(slab_page(sp));
> slob_free_pages(b, 0);
> return;
> }
>
>>
>> > diff --git a/mm/slob.c b/mm/slob.c
>> > index d3512bcc3141..cf669f03440f 100644
>> > --- a/mm/slob.c
>> > +++ b/mm/slob.c
>> > @@ -358,8 +358,8 @@ static void *slob_alloc(size_t size, gfp_t gfp, int a
>> > lign, int node,
>> > b = slob_new_pages(gfp & ~__GFP_ZERO, 0, node);
>> > if (!b)
>> > return NULL;
>> > + __SetPageSlab(virt_to_page(b));
>> > sp = virt_to_slab(b);
>> > - __SetPageSlab(slab_page(sp));
>> >
>> > spin_lock_irqsave(&slob_lock, flags);
>> > sp->units = SLOB_UNITS(PAGE_SIZE);
>> >
>> > Thanks,
>> > Hyeonggon.
>> >
>> >>
>> >> spin_lock_irqsave(&slob_lock, flags);
>> >> sp->units = SLOB_UNITS(PAGE_SIZE);
>> >> @@ -381,7 +381,7 @@ static void *slob_alloc(size_t size, gfp_t gfp, int align, int node,
>> >> */
>> >> static void slob_free(void *block, int size)
>> >> {
>> >> - struct page *sp;
>> >> + struct slab *sp;
>> >> slob_t *prev, *next, *b = (slob_t *)block;
>> >> slobidx_t units;
>> >> unsigned long flags;
>> >> @@ -391,7 +391,7 @@ static void slob_free(void *block, int size)
>> >> return;
>> >> BUG_ON(!size);
>> >>
>> >> - sp = virt_to_page(block);
>> >> + sp = virt_to_slab(block);
>> >> units = SLOB_UNITS(size);
>> >>
>> >> spin_lock_irqsave(&slob_lock, flags);
>> >> @@ -401,8 +401,8 @@ static void slob_free(void *block, int size)
>> >> if (slob_page_free(sp))
>> >> clear_slob_page_free(sp);
>> >> spin_unlock_irqrestore(&slob_lock, flags);
>> >> - __ClearPageSlab(sp);
>> >> - page_mapcount_reset(sp);
>> >> + __ClearPageSlab(slab_page(sp));
>> >> + page_mapcount_reset(slab_page(sp));
>> >> slob_free_pages(b, 0);
>> >> return;
>> >> }
>> >> --
>> >> 2.33.1
>> >>
>> >>
>>
