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Mon, 7 Nov 2022 14:20:35 +0000 (UTC) Date: Mon, 7 Nov 2022 15:20:34 +0100 From: Petr Mladek To: Andy Shevchenko Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>, linux-mm@kvack.org, Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Vlastimil Babka , Naoya Horiguchi , Miaohe Lin , Matthew Wilcox , Minchan Kim , Mel Gorman , Andrea Arcangeli , Dan Williams , Hugh Dickins , Muchun Song , David Hildenbrand , Steven Rostedt , Sergey Senozhatsky , Rasmus Villemoes , Jonathan Corbet , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC v2 3/3] mm, printk: introduce new format %pGt for page_type Message-ID: References: <20221106140355.294845-1-42.hyeyoo@gmail.com> <20221106140355.294845-4-42.hyeyoo@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=EQW19GhD; spf=pass (imf28.hostedemail.com: domain of pmladek@suse.com designates 195.135.220.29 as permitted sender) smtp.mailfrom=pmladek@suse.com; 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spf=pass (imf28.hostedemail.com: domain of pmladek@suse.com designates 195.135.220.29 as permitted sender) smtp.mailfrom=pmladek@suse.com; dmarc=pass (policy=quarantine) header.from=suse.com X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 58337C000B X-Stat-Signature: e51zq8ypu8iy9dakeri6ekjpie1zo4e3 X-HE-Tag: 1667830840-991337 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: On Mon 2022-11-07 13:18:52, Andy Shevchenko wrote: > On Sun, Nov 06, 2022 at 11:03:55PM +0900, Hyeonggon Yoo wrote: > > dump_page() uses %pGp format to print 'flags' field of struct page. > > As some page flags (e.g. PG_buddy, see page-flags.h for more details) > > are set in page_type field, introduce %pGt format which provides > > human readable output of page_type. And use it in dump_page(). > > > > Note that the sense of bits are different in page_type. if page_type is > > 0xffffffff, no flags are set. if PG_slab (0x00100000) flag is set, > > page_type is 0xffefffff. Clearing a bit means we set the bit. Bits in > > page_type are inverted when printing type names. > > > > Below is examples of dump_page(). One is just after alloc_pages() and > > the other is after __SetPageSlab(). > > > > [ 1.814728] page:ffffea000415e200 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x105788 > > [ 1.815961] flags: 0x17ffffc0000000(node=0|zone=2|lastcpupid=0x1fffff) > > > [ 1.816443] page_type: 0xffffffff() > > Why do we have empty parentheses? I would expect either something there, or no > parentheses at all. This looks fine. format_page_flags() does the same for %pGp. > ... > > > + %pGt 0xffefffff(slab) > > No space before ( ? Also looks fine. %pGp does the same. > ... > > > +static > > +char *format_page_type(char *buf, char *end, unsigned int page_type) > > +{ > > + if (!(page_type & PAGE_TYPE_BASE)) > > + return string(buf, end, "no type for user-mapped page", default_str_spec); > > It's too long, can we make it shorten? I wonder if it would help to write the value. Something like: page_type: 0x0ace5768(no type) That said. I am not familiar with the page types and am not sure about the semantic of this value. MM people should decide what they want to see in this case. > ... > > > pr_warn("%sflags: %pGp%s\n", type, &head->flags, > > page_cma ? " CMA" : ""); > > + pr_warn("page_type: %pGt\n", &head->page_type); > > + > > print_hex_dump(KERN_WARNING, "raw: ", DUMP_PREFIX_NONE, 32, > > sizeof(unsigned long), page, > > sizeof(struct page), false); > > diff --git a/mm/internal.h b/mm/internal.h > > index cb4c663a714e..956eaa9f12c0 100644 > > --- a/mm/internal.h > > +++ b/mm/internal.h > > @@ -773,6 +773,7 @@ static inline void flush_tlb_batched_pending(struct mm_struct *mm) > > #endif /* CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH */ > > > > extern const struct trace_print_flags pageflag_names[]; > > +extern const struct trace_print_flags pagetype_names[]; > > extern const struct trace_print_flags vmaflag_names[]; > > extern const struct trace_print_flags gfpflag_names[]; > > I would split this to a separate change, but it's up to PRINTK maintainers. I guess that you are talking about the line: + pr_warn("page_type: %pGt\n", &head->page_type); Yes, it would be better to have implementation of %pGt modifier in one patch and add the user in another one. Best Regards, Petr