On Fri, Dec 10, 2021 at 07:09:56PM +0100, Vlastimil Babka wrote:
> 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!
>
You're welcome! :)
> > 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.
>
Yeah, It is better to be done as separate patch.
I'll send it as a patch.
Thanks,
Hyeonggon
> > 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
> >> >>
> >> >>
> >>
>
