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>
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.
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
> >>
> >>
>
