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SubjectRe: [PATCH v3 3/7] slob: Use slab_list instead of lru
On Thu, Mar 14, 2019 at 06:52:25PM +0000, Roman Gushchin wrote:
> On Thu, Mar 14, 2019 at 04:31:31PM +1100, Tobin C. Harding wrote:
> > Currently we use the page->lru list for maintaining lists of slabs. We
> > have a list_head in the page structure (slab_list) that can be used for
> > this purpose. Doing so makes the code cleaner since we are not
> > overloading the lru list.
> >
> > The slab_list is part of a union within the page struct (included here
> > stripped down):
> >
> > union {
> > struct { /* Page cache and anonymous pages */
> > struct list_head lru;
> > ...
> > };
> > struct {
> > dma_addr_t dma_addr;
> > };
> > struct { /* slab, slob and slub */
> > union {
> > struct list_head slab_list;
> > struct { /* Partial pages */
> > struct page *next;
> > int pages; /* Nr of pages left */
> > int pobjects; /* Approximate count */
> > };
> > };
> > ...
> >
> > Here we see that slab_list and lru are the same bits. We can verify
> > that this change is safe to do by examining the object file produced from
> > slob.c before and after this patch is applied.
> >
> > Steps taken to verify:
> >
> > 1. checkout current tip of Linus' tree
> >
> > commit a667cb7a94d4 ("Merge branch 'akpm' (patches from Andrew)")
> >
> > 2. configure and build (select SLOB allocator)
> >
> > CONFIG_SLOB=y
> > CONFIG_SLAB_MERGE_DEFAULT=y
> >
> > 3. dissasemble object file `objdump -dr mm/slub.o > before.s
> > 4. apply patch
> > 5. build
> > 6. dissasemble object file `objdump -dr mm/slub.o > after.s
> > 7. diff before.s after.s
> >
> > Use slab_list list_head instead of the lru list_head for maintaining
> > lists of slabs.
> >
> > Reviewed-by: Roman Gushchin <guro@fb.com>
> > Signed-off-by: Tobin C. Harding <tobin@kernel.org>
> > ---
> > mm/slob.c | 8 ++++----
> > 1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/mm/slob.c b/mm/slob.c
> > index 39ad9217ffea..94486c32e0ff 100644
> > --- a/mm/slob.c
> > +++ b/mm/slob.c
> > @@ -112,13 +112,13 @@ static inline int slob_page_free(struct page *sp)
> >
> > static void set_slob_page_free(struct page *sp, struct list_head *list)
> > {
> > - list_add(&sp->lru, list);
> > + list_add(&sp->slab_list, list);
> > __SetPageSlobFree(sp);
> > }
> >
> > static inline void clear_slob_page_free(struct page *sp)
> > {
> > - list_del(&sp->lru);
> > + list_del(&sp->slab_list);
> > __ClearPageSlobFree(sp);
> > }
> >
> > @@ -282,7 +282,7 @@ static void *slob_alloc(size_t size, gfp_t gfp, int align, int node)
> >
> > spin_lock_irqsave(&slob_lock, flags);
> > /* Iterate through each partially free page, try to find room */
> > - list_for_each_entry(sp, slob_list, lru) {
> > + list_for_each_entry(sp, slob_list, slab_list) {
> > #ifdef CONFIG_NUMA
> > /*
> > * If there's a node specification, search for a partial
>
>
> Hi Tobin!
>
> How about list_rotate_to_front(&next->lru, slob_list) from the previous patch?
> Shouldn't it use slab_list instead of lru too?

I'll let this sit for a day or two in case we get any more comments on
the list.h stuff then do another version ready for US Monday morning.

Thanks again,
Tobin.

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