linux-kernel - Re: [PATCHv9 02/14] mm: Add support for unaccepted memory

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Date:   Mon, 3 Apr 2023 13:02:44 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joerg Roedel <jroedel@...e.de>,
        Ard Biesheuvel <ardb@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Dario Faggioli <dfaggioli@...e.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Mike Rapoport <rppt@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        marcelo.cerri@...onical.com, tim.gardner@...onical.com,
        khalid.elmously@...onical.com, philip.cox@...onical.com,
        aarcange@...hat.com, peterx@...hat.com, x86@...nel.org,
        linux-mm@...ck.org, linux-coco@...ts.linux.dev,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mike Rapoport <rppt@...ux.ibm.com>
Subject: Re: [PATCHv9 02/14] mm: Add support for unaccepted memory

On Mon, Apr 03, 2023 at 11:26:53AM +0200, Vlastimil Babka wrote:
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > Acked-by: Mike Rapoport <rppt@...ux.ibm.com>	# memblock
> 
> Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

Thanks!

> Just a small suggestion below:
> 
> > +
> > +static bool try_to_accept_memory(struct zone *zone, unsigned int order)
> > +{
> > +	long to_accept;
> > +	int ret = false;
> > +
> > +	if (!static_branch_unlikely(&zones_with_unaccepted_pages))
> > +		return false;
> 
> 
> This potentially (depends on what compiler decides) means we'll call this
> function just to skip the static branch. OTOH forcing it as inline would be
> wasteful too. So I'd split that away and make the callers do that static
> branch check inline. Just as deferred_pages_enabled() is used.

Like this?

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 07e16e9b49c4..80fe5e4b6cca 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -390,6 +390,7 @@ EXPORT_SYMBOL(nr_online_nodes);
 static bool page_contains_unaccepted(struct page *page, unsigned int order);
 static void accept_page(struct page *page, unsigned int order);
 static bool try_to_accept_memory(struct zone *zone, unsigned int order);
+static inline bool has_unaccepted_memory(void);
 static bool __free_unaccepted(struct page *page);
 
 int page_group_by_mobility_disabled __read_mostly;
@@ -3464,8 +3465,10 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
 				       gfp_mask)) {
 			int ret;
 
-			if (try_to_accept_memory(zone, order))
-				goto try_this_zone;
+			if (has_unaccepted_memory()) {
+				if (try_to_accept_memory(zone, order))
+					goto try_this_zone;
+			}
 
 #ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
 			/*
@@ -3519,8 +3522,10 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
 
 			return page;
 		} else {
-			if (try_to_accept_memory(zone, order))
-				goto try_this_zone;
+			if (has_unaccepted_memory()) {
+				if (try_to_accept_memory(zone, order))
+					goto try_this_zone;
+			}
 
 #ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
 			/* Try again if zone has deferred pages */
@@ -7302,9 +7307,6 @@ static bool try_to_accept_memory(struct zone *zone, unsigned int order)
 	long to_accept;
 	int ret = false;
 
-	if (!static_branch_unlikely(&zones_with_unaccepted_pages))
-		return false;
-
 	/* How much to accept to get to high watermark? */
 	to_accept = high_wmark_pages(zone) -
 		    (zone_page_state(zone, NR_FREE_PAGES) -
@@ -7321,6 +7323,11 @@ static bool try_to_accept_memory(struct zone *zone, unsigned int order)
 	return ret;
 }
 
+static inline bool has_unaccepted_memory(void)
+{
+	return static_branch_unlikely(&zones_with_unaccepted_pages);
+}
+
 static bool __free_unaccepted(struct page *page)
 {
 	struct zone *zone = page_zone(page);
@@ -7398,6 +7405,11 @@ static bool try_to_accept_memory(struct zone *zone, unsigned int order)
 	return false;
 }
 
+static inline bool has_unaccepted_memory(void)
+{
+	return false;
+}
+
 static bool __free_unaccepted(struct page *page)
 {
 	BUILD_BUG();
-- 
  Kiryl Shutsemau / Kirill A. Shutemov