linux-kernel - Re: [PATCH mm-unstable v2 2/3] mm/cma: add cma_{alloc,free}

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Message-ID: <ZtXwM0wqqAPygDXs@google.com>
Date: Mon, 2 Sep 2024 11:04:51 -0600
From: Yu Zhao <yuzhao@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
	Muchun Song <muchun.song@...ux.dev>
Cc: "Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Zi Yan <ziy@...dia.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH mm-unstable v2 2/3] mm/cma: add cma_{alloc,free}_folio()

On Thu, Aug 22, 2024 at 11:24:14AM -0600, Yu Zhao wrote:
> On Tue, Aug 13, 2024 at 09:54:50PM -0600, Yu Zhao wrote:
> > With alloc_contig_range() and free_contig_range() supporting large
> > folios, CMA can allocate and free large folios too, by
> > cma_alloc_folio() and cma_free_folio().
> > 
> > Signed-off-by: Yu Zhao <yuzhao@...gle.com>
> > ---
> >  include/linux/cma.h | 16 +++++++++++++
> >  mm/cma.c            | 55 ++++++++++++++++++++++++++++++++-------------
> >  2 files changed, 56 insertions(+), 15 deletions(-)
> > 
> > diff --git a/include/linux/cma.h b/include/linux/cma.h
> > index 9db877506ea8..d15b64f51336 100644
> > --- a/include/linux/cma.h
> > +++ b/include/linux/cma.h
> > @@ -52,4 +52,20 @@ extern bool cma_release(struct cma *cma, const struct page *pages, unsigned long
> >  extern int cma_for_each_area(int (*it)(struct cma *cma, void *data), void *data);
> >  
> >  extern void cma_reserve_pages_on_error(struct cma *cma);
> > +
> > +#ifdef CONFIG_CMA
> > +struct folio *cma_alloc_folio(struct cma *cma, int order, gfp_t gfp);
> > +bool cma_free_folio(struct cma *cma, const struct folio *folio);
> > +#else
> > +static inline struct folio *cma_alloc_folio(struct cma *cma, int order, gfp_t gfp)
> > +{
> > +	return NULL;
> > +}
> > +
> > +static inline bool cma_free_folio(struct cma *cma, const struct folio *folio)
> > +{
> > +	return false;
> > +}
> > +#endif
> > +
> >  #endif
> > diff --git a/mm/cma.c b/mm/cma.c
> > index 95d6950e177b..4354823d28cf 100644
> > --- a/mm/cma.c
> > +++ b/mm/cma.c
> > @@ -403,18 +403,8 @@ static void cma_debug_show_areas(struct cma *cma)
> >  	spin_unlock_irq(&cma->lock);
> >  }
> >  
> > -/**
> > - * cma_alloc() - allocate pages from contiguous area
> > - * @cma:   Contiguous memory region for which the allocation is performed.
> > - * @count: Requested number of pages.
> > - * @align: Requested alignment of pages (in PAGE_SIZE order).
> > - * @no_warn: Avoid printing message about failed allocation
> > - *
> > - * This function allocates part of contiguous memory on specific
> > - * contiguous memory area.
> > - */
> > -struct page *cma_alloc(struct cma *cma, unsigned long count,
> > -		       unsigned int align, bool no_warn)
> > +static struct page *__cma_alloc(struct cma *cma, unsigned long count,
> > +				unsigned int align, gfp_t gfp)
> >  {
> >  	unsigned long mask, offset;
> >  	unsigned long pfn = -1;
> > @@ -463,8 +453,7 @@ struct page *cma_alloc(struct cma *cma, unsigned long count,
> >  
> >  		pfn = cma->base_pfn + (bitmap_no << cma->order_per_bit);
> >  		mutex_lock(&cma_mutex);
> > -		ret = alloc_contig_range(pfn, pfn + count, MIGRATE_CMA,
> > -				     GFP_KERNEL | (no_warn ? __GFP_NOWARN : 0));
> > +		ret = alloc_contig_range(pfn, pfn + count, MIGRATE_CMA, gfp);
> >  		mutex_unlock(&cma_mutex);
> >  		if (ret == 0) {
> >  			page = pfn_to_page(pfn);
> > @@ -494,7 +483,7 @@ struct page *cma_alloc(struct cma *cma, unsigned long count,
> >  			page_kasan_tag_reset(nth_page(page, i));
> >  	}
> >  
> > -	if (ret && !no_warn) {
> > +	if (ret && !(gfp & __GFP_NOWARN)) {
> >  		pr_err_ratelimited("%s: %s: alloc failed, req-size: %lu pages, ret: %d\n",
> >  				   __func__, cma->name, count, ret);
> >  		cma_debug_show_areas(cma);
> > @@ -513,6 +502,34 @@ struct page *cma_alloc(struct cma *cma, unsigned long count,
> >  	return page;
> >  }
> >  
> > +/**
> > + * cma_alloc() - allocate pages from contiguous area
> > + * @cma:   Contiguous memory region for which the allocation is performed.
> > + * @count: Requested number of pages.
> > + * @align: Requested alignment of pages (in PAGE_SIZE order).
> > + * @no_warn: Avoid printing message about failed allocation
> > + *
> > + * This function allocates part of contiguous memory on specific
> > + * contiguous memory area.
> > + */
> > +struct page *cma_alloc(struct cma *cma, unsigned long count,
> > +		       unsigned int align, bool no_warn)
> > +{
> > +	return __cma_alloc(cma, count, align, GFP_KERNEL | (no_warn ? __GFP_NOWARN : 0));
> > +}
> > +
> > +struct folio *cma_alloc_folio(struct cma *cma, int order, gfp_t gfp)
> > +{
> > +	struct page *page;
> > +
> > +	if (WARN_ON(!order || !(gfp | __GFP_COMP)))
> 
> And here too. Thank you.
> 
> diff --git a/mm/cma.c b/mm/cma.c
> index 4354823d28cf..2d9fae939283 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -522,7 +522,7 @@ struct folio *cma_alloc_folio(struct cma *cma, int order, gfp_t gfp)
>  {
>  	struct page *page;
>  
> -	if (WARN_ON(!order || !(gfp | __GFP_COMP)))
> +	if (WARN_ON(!order || !(gfp & __GFP_COMP)))
>  		return NULL;
>  
>  	page = __cma_alloc(cma, 1 << order, order, gfp);

And the following instead of the above, if we don't want to warn the
potential bug.

diff --git a/mm/cma.c b/mm/cma.c
index 2d9fae939283..00c30dcee200 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -522,10 +522,7 @@ struct folio *cma_alloc_folio(struct cma *cma, int order, gfp_t gfp)
 {
 	struct page *page;
 
-	if (WARN_ON(!order || !(gfp & __GFP_COMP)))
-		return NULL;
-
-	page = __cma_alloc(cma, 1 << order, order, gfp);
+	page = __cma_alloc(cma, 1 << order, order, gfp | __GFP_COMP);
 
 	return page ? page_folio(page) : NULL;
 }