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Message-ID: <20210323204940.GB52881@pc638.lan>
Date: Tue, 23 Mar 2021 21:49:40 +0100
From: Uladzislau Rezki <urezki@...il.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: Uladzislau Rezki <urezki@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Christoph Lameter <cl@...ux.com>,
Pekka Enberg <penberg@...nel.org>,
David Rientjes <rientjes@...gle.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Nicholas Piggin <npiggin@...il.com>
Subject: Re: [PATCH 2/2] mm/vmalloc: Use kvmalloc to allocate the table of
pages
On Tue, Mar 23, 2021 at 02:07:22PM +0000, Matthew Wilcox wrote:
> On Tue, Mar 23, 2021 at 02:39:48PM +0100, Uladzislau Rezki wrote:
> > On Tue, Mar 23, 2021 at 12:39:13PM +0000, Matthew Wilcox wrote:
> > > On Tue, Mar 23, 2021 at 01:04:36PM +0100, Uladzislau Rezki wrote:
> > > > On Mon, Mar 22, 2021 at 11:03:11PM +0000, Matthew Wilcox wrote:
> > > > > I suspect the vast majority of the time is spent calling alloc_pages_node()
> > > > > 1024 times. Have you looked at Mel's patch to do ... well, exactly what
> > > > > vmalloc() wants?
> > > > >
> > > > <snip>
> > > > - __vmalloc_node_range
> > > > - 45.25% __alloc_pages_nodemask
> > > > - 37.59% get_page_from_freelist
> > > [...]
> > > > - 44.61% 0xffffffffc047348d
> > > > - __vunmap
> > > > - 35.56% free_unref_page
> > >
> > > Hmm! I hadn't been thinking about the free side of things.
> > > Does this make a difference?
> > >
> > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > > index 4f5f8c907897..61d5b769fea0 100644
> > > --- a/mm/vmalloc.c
> > > +++ b/mm/vmalloc.c
> > > @@ -2277,16 +2277,8 @@ static void __vunmap(const void *addr, int deallocate_pages)
> > > vm_remove_mappings(area, deallocate_pages);
> > >
> > > if (deallocate_pages) {
> > > - int i;
> > > -
> > > - for (i = 0; i < area->nr_pages; i++) {
> > > - struct page *page = area->pages[i];
> > > -
> > > - BUG_ON(!page);
> > > - __free_pages(page, 0);
> > > - }
> > > + release_pages(area->pages, area->nr_pages);
> > > atomic_long_sub(area->nr_pages, &nr_vmalloc_pages);
> > > -
> > > kvfree(area->pages);
> > > }
> > >
> > Will check it today!
> >
> > > release_pages does a bunch of checks that are unnecessary ... we could
> > > probably just do:
> > >
> > > LIST_HEAD(pages_to_free);
> > >
> > > for (i = 0; i < area->nr_pages; i++) {
> > > struct page *page = area->pages[i];
> > > if (put_page_testzero(page))
> > > list_add(&page->lru, &pages_to_free);
> > > }
> > > free_unref_page_list(&pages_to_free);
> > >
> > > but let's see if the provided interface gets us the performance we want.
> > >
> > > > Reviewed-by: Uladzislau Rezki (Sony) <urezki@...il.com>
> > > >
> > > > Thanks!
> > >
> > > Thank you!
> > You are welcome. A small nit:
> >
> > CC mm/vmalloc.o
> > mm/vmalloc.c: In function ‘__vmalloc_area_node’:
> > mm/vmalloc.c:2492:14: warning: passing argument 4 of ‘kvmalloc_node_caller’ makes integer from pointer without a cast [-Wint-conversion]
> > area->caller);
> > ~~~~^~~~~~~~
> > In file included from mm/vmalloc.c:12:
> > ./include/linux/mm.h:782:7: note: expected ‘long unsigned int’ but argument is of type ‘const void *’
> > void *kvmalloc_node_caller(size_t size, gfp_t flags, int node,
>
> Oh, thank you! I confused myself by changing the type halfway through.
> vmalloc() uses void * to match __builtin_return_address while most
> of the rest of the kernel uses unsigned long to match _RET_IP_.
> I'll submit another patch to convert vmalloc to use _RET_IP_.
>
Thanks!
> > As for the bulk-array interface. I have checked the:
> >
> > git://git.kernel.org/pub/scm/linux/kernel/git/mel/linux.git mm-bulk-rebase-v6r2
> >
> > applied the patch that is in question + below one:
> >
> > <snip>
> > @@ -2503,25 +2498,13 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
> > area->pages = pages;
> > area->nr_pages = nr_pages;
> >
> > - for (i = 0; i < area->nr_pages; i++) {
> > - struct page *page;
> > -
> > - if (node == NUMA_NO_NODE)
> > - page = alloc_page(gfp_mask);
> > - else
> > - page = alloc_pages_node(node, gfp_mask, 0);
> > -
> > - if (unlikely(!page)) {
> > - /* Successfully allocated i pages, free them in __vfree() */
> > - area->nr_pages = i;
> > - atomic_long_add(area->nr_pages, &nr_vmalloc_pages);
> > - goto fail;
> > - }
> > - area->pages[i] = page;
> > - if (gfpflags_allow_blocking(gfp_mask))
> > - cond_resched();
> > + ret = alloc_pages_bulk_array(gfp_mask, area->nr_pages, area->pages);
> > + if (ret == nr_pages)
> > + atomic_long_add(area->nr_pages, &nr_vmalloc_pages);
> > + else {
> > + area->nr_pages = ret;
> > + goto fail;
> > }
> > - atomic_long_add(area->nr_pages, &nr_vmalloc_pages);
> > <snip>
> >
> > single CPU, 4MB allocation, 1000000 avg: 70639437 usec
> > single CPU, 4MB allocation, 1000000 avg: 89218654 usec
> >
> > and now we get ~21% delta. That is very good :)
>
> Amazing! That's great news for Mel's patch as well as the kvmalloc
> change.
>
Cool! I am glad if it gives some points to the bulk-array interface :)
--
Vlad Rezki
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