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Shutemov" , David Hildenbrand Subject: Re: [PATCH] [RFC] mm/mm_init.c: simplify logic of deferred_[init|free]_pages Message-ID: References: <20240605010742.11667-1-richard.weiyang@gmail.com> <20240610145457.zvgw773n53twa7my@master> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240610145457.zvgw773n53twa7my@master> X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 5B7F91A0021 X-Stat-Signature: 9mnzxwm6ys3su57gch3x61fiws8knz3w X-HE-Tag: 1718100038-797065 X-HE-Meta: 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 ZUgvFlOr rN4+SGafqB31Dibcge+yl2Uy0O5KVLevhSafP8s3REkpeKgIjBC19mqwegXdyK6L6w8ergW5j+4oX0lVwFfIEO/yKP4vVmHPMKWdXUweGI9q7uvGFb/EsPdSZ+IK+8XoBqnKRlfeR54N4icKFO6dmcB4e6OCiDar9GgQ5ulSfYYl20WFXosnQrPZrDnRApx4WzxHmOcdpd1a7jqUPxwWNcLFNXy/cTKBP/RjzlFkj5vYsSbayY2X4RIKnLr+o0SEDF82WHFuf6zVKNBZghh9DjLyRrr3owIwz4zKuNaffKj5q+iTkmT2u2RfeYjF3wACArvRMNBjBZ1oNzXeicqFXNB0wqLgBwWt9ILnuiff1YM7i6UqawuxvshhDBSeaf+vjSJaBwv6aFuqOOuxNuxyBKP3q+fccYt+D6Iw0hiih5+uAqjcLrlVZ/x35WQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Jun 10, 2024 at 02:54:57PM +0000, Wei Yang wrote: > On Mon, Jun 10, 2024 at 09:40:33AM +0300, Mike Rapoport wrote: > >On Wed, Jun 05, 2024 at 01:07:42AM +0000, Wei Yang wrote: > >> Function deferred_[init|free]_pages are only used in > >> deferred_init_maxorder(), which makes sure the range to init/free is > >> within MAX_ORDER_NR_PAGES size. > >> > >> With this knowledge, we can simplify these two functions. Since > >> > >> * only the first pfn could be IS_MAX_ORDER_ALIGNED() > > > >No, the first pfn is not necessarily IS_MAX_ORDER_ALIGNED(). Start pfn is a > >beginning of a region in memblock.memory, and there's no guarantee on it's > >alignment. > > > > Yes, I mean only the first pfn is possible to be IS_MAX_ORDER_ALIGNED(), not > must be IS_MAX_ORDER_ALIGNED(). > > The range passed to deferred_[init|free]_pages must be within one > MAX_ORDER_NR_PAGES. If the first pfn is not IS_MAX_ORDER_ALIGNED(), others > could not be IS_MAX_ORDER_ALIGNED(). > > Currently these two functions would iterate all pfn, and check > IS_MAX_ORDER_ALIGNED() to break init|free on each MAX_ORDER_NR_PAGES. But this > is only possible and necessary on the first pfn. Thinking more about it, it looks to me that deferred_pfn_valid() cannot ever return false. The ranges that are passed to deferred_{free,init}_pages are always from memblock.memory and we allocate the memory map to cover memblock.memory with at least MAX_ORDER_NR_PAGES alignment. So I don't see how pfn_valid() in deferred_pfn_valid() may ever return false. > >> Signed-off-by: Wei Yang > >> CC: Kirill A. Shutemov > >> CC: Mike Rapoport (IBM) > >> CC: David Hildenbrand > >> > >> --- > >> But my question is why we just test pfn_valid for the > >> IS_MAX_ORDER_ALIGNED pfn? I thought we should test pfn_valid for each > >> pfn until the first one in MAX_ORDER pages. Do I miss something? > >> --- > >> mm/mm_init.c | 43 ++++++++++++++----------------------------- > >> 1 file changed, 14 insertions(+), 29 deletions(-) > >> > >> diff --git a/mm/mm_init.c b/mm/mm_init.c > >> index bbaf3a2c1cfd..6a4adf9e7d9a 100644 > >> --- a/mm/mm_init.c > >> +++ b/mm/mm_init.c > >> @@ -1970,21 +1970,10 @@ static inline bool __init deferred_pfn_valid(unsigned long pfn) > >> static void __init deferred_free_pages(unsigned long pfn, > >> unsigned long end_pfn) > >> { > >> - unsigned long nr_free = 0; > >> - > >> - for (; pfn < end_pfn; pfn++) { > >> - if (!deferred_pfn_valid(pfn)) { > >> - deferred_free_range(pfn - nr_free, nr_free); > >> - nr_free = 0; > >> - } else if (IS_MAX_ORDER_ALIGNED(pfn)) { > >> - deferred_free_range(pfn - nr_free, nr_free); > >> - nr_free = 1; > >> - } else { > >> - nr_free++; > >> - } > >> - } > >> - /* Free the last block of pages to allocator */ > >> - deferred_free_range(pfn - nr_free, nr_free); > >> + if (!deferred_pfn_valid(pfn)) > >> + pfn++; > >> + > >> + deferred_free_range(pfn, end_pfn - pfn); > >> } > >> > >> /* > >> @@ -1992,27 +1981,23 @@ static void __init deferred_free_pages(unsigned long pfn, > >> * by performing it only once every MAX_ORDER_NR_PAGES. > >> * Return number of pages initialized. > >> */ > >> -static unsigned long __init deferred_init_pages(struct zone *zone, > >> - unsigned long pfn, > >> - unsigned long end_pfn) > >> +static unsigned long __init deferred_init_pages(struct zone *zone, > >> + unsigned long pfn, > >> + unsigned long end_pfn) > >> { > >> int nid = zone_to_nid(zone); > >> unsigned long nr_pages = 0; > >> int zid = zone_idx(zone); > >> struct page *page = NULL; > >> > >> - for (; pfn < end_pfn; pfn++) { > >> - if (!deferred_pfn_valid(pfn)) { > >> - page = NULL; > >> - continue; > >> - } else if (!page || IS_MAX_ORDER_ALIGNED(pfn)) { > >> - page = pfn_to_page(pfn); > >> - } else { > >> - page++; > >> - } > >> + if (!deferred_pfn_valid(pfn)) > >> + pfn++; > >> + > >> + page = pfn_to_page(pfn); > >> + nr_pages = end_pfn - pfn; > >> + > >> + for (; pfn < end_pfn; pfn++, page++) > >> __init_single_page(page, pfn, zid, nid); > >> - nr_pages++; > >> - } > >> return nr_pages; > >> } > >> > >> -- > >> 2.34.1 > >> > > > >-- > >Sincerely yours, > >Mike. > > -- > Wei Yang > Help you, Help me -- Sincerely yours, Mike.