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Wed, 10 Feb 2021 07:39:57 -0800 (PST) MIME-Version: 1.0 References: <20210209105613.42747-1-laoar.shao@gmail.com> <20210209105613.42747-4-laoar.shao@gmail.com> In-Reply-To: From: Yafang Shao Date: Wed, 10 Feb 2021 23:39:21 +0800 Message-ID: Subject: Re: [PATCH v4 3/3] vsprintf: dump full information of page flags in pGp To: Petr Mladek Cc: Matthew Wilcox , Andy Shevchenko , David Hildenbrand , Miaohe Lin , Vlastimil Babka , Christoph Lameter , penberg@kernel.org, David Rientjes , iamjoonsoo.kim@lge.com, Andrew Morton , Steven Rostedt , Sergey Senozhatsky , Joe Perches , Linux MM , LKML Content-Type: text/plain; charset="UTF-8" X-Stat-Signature: yojkfxyg8jby9mk6ggocj9387cyt5h5q X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 9F5CD407F8D8 Received-SPF: none (gmail.com>: No applicable sender policy available) receiver=imf10; identity=mailfrom; envelope-from=""; helo=mail-il1-f170.google.com; client-ip=209.85.166.170 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1612971597-151470 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 Wed, Feb 10, 2021 at 8:51 PM Petr Mladek wrote: > > On Wed 2021-02-10 00:21:37, Yafang Shao wrote: > > On Tue, Feb 9, 2021 at 9:53 PM Petr Mladek wrote: > > > > > > On Tue 2021-02-09 18:56:13, Yafang Shao wrote: > > > > Currently the pGp only shows the names of page flags, rather than > > > > the full information including section, node, zone, last cpupid and > > > > kasan tag. While it is not easy to parse these information manually > > > > because there're so many flavors. Let's interpret them in pGp as well. > > > > > > > > To be compitable with the existed format of pGp, the new introduced ones > > > > also use '|' as the separator, then the user tools parsing pGp won't > > > > need to make change, suggested by Matthew. The new information is > > > > tracked onto the end of the existed one. > > > > > > > > On example of the output in mm/slub.c as follows, > > > > - Before the patch, > > > > [ 6343.396602] Slab 0x000000004382e02b objects=33 used=3 fp=0x000000009ae06ffc flags=0x17ffffc0010200(slab|head) > > > > > > > > - After the patch, > > > > [ 8838.835456] Slab 0x000000002828b78a objects=33 used=3 fp=0x00000000d04efc88 flags=0x17ffffc0010200(slab|head|node=0|zone=2|lastcpupid=0x1fffff) > > > > > > > > The documentation and test cases are also updated. The output of the > > > > test cases as follows, > > > > [ 501.485081] test_printf: loaded. > > > > [ 501.485768] test_printf: all 388 tests passed > > > > [ 501.488762] test_printf: unloaded. > > > > > > > > > > > diff --git a/lib/vsprintf.c b/lib/vsprintf.c > > > > index 14c9a6af1b23..3f26611adb34 100644 > > > > --- a/lib/vsprintf.c > > > > +++ b/lib/vsprintf.c > > > > @@ -1916,6 +1916,66 @@ char *format_flags(char *buf, char *end, unsigned long flags, > > > > return buf; > > > > } > > > > > > > > +struct page_flags_layout { > > > > + int width; > > > > + int shift; > > > > + int mask; > > > > + const struct printf_spec *spec; > > > > + const char *name; > > > > +}; > > > > + > > > > +static const struct page_flags_layout pfl[] = { > > > > + {SECTIONS_WIDTH, SECTIONS_PGSHIFT, SECTIONS_MASK, > > > > + &default_dec_spec, "section"}, > > > > + {NODES_WIDTH, NODES_PGSHIFT, NODES_MASK, > > > > + &default_dec_spec, "node"}, > > > > + {ZONES_WIDTH, ZONES_PGSHIFT, ZONES_MASK, > > > > + &default_dec_spec, "zone"}, > > > > + {LAST_CPUPID_WIDTH, LAST_CPUPID_PGSHIFT, LAST_CPUPID_MASK, > > > > + &default_flag_spec, "lastcpupid"}, > > > > + {KASAN_TAG_WIDTH, KASAN_TAG_PGSHIFT, KASAN_TAG_MASK, > > > > + &default_flag_spec, "kasantag"}, > > > > +}; > > > > + > > > > +static > > > > +char *format_page_flags(char *buf, char *end, unsigned long flags) > > > > +{ > > > > + DECLARE_BITMAP(mask, ARRAY_SIZE(pfl)); > > > > + unsigned long last; > > > > + int i; > > > > + > > > > + if (flags & (BIT(NR_PAGEFLAGS) - 1)) { > > > > + if (buf < end) > > > > + *buf = '|'; > > > > + buf++; > > > > + } > > > > > > This is far from obvious. You print '|' here because you printed > > > something somewhere else. See below. > > > > > > > + > > > > + for (i = 0; i < ARRAY_SIZE(pfl); i++) > > > > + __assign_bit(i, mask, pfl[i].width); > > > > > > The bitmap looks like an overkill. If I get it correctly, it is a > > > tricky way to handle only flags defined by the used build > > > configuration. See below. > > > > > > > + last = find_last_bit(mask, ARRAY_SIZE(pfl)); > > > > + > > > > + for_each_set_bit(i, mask, ARRAY_SIZE(pfl)) { > > > > + /* Format: Flag Name + '=' (equals sign) + Number + '|' (separator) */ > > > > + buf = string(buf, end, pfl[i].name, *pfl[i].spec); > > > > + > > > > + if (buf < end) > > > > + *buf = '='; > > > > + buf++; > > > > + buf = number(buf, end, (flags >> pfl[i].shift) & pfl[i].mask, > > > > + *pfl[i].spec); > > > > + > > > > + /* No separator for the last entry */ > > > > + if (i != last) { > > > > + if (buf < end) > > > > + *buf = '|'; > > > > + buf++; > > > > + } > > > > + } > > > > + > > > > + return buf; > > > > +} > > > > + > > > > static noinline_for_stack > > > > char *flags_string(char *buf, char *end, void *flags_ptr, > > > > struct printf_spec spec, const char *fmt) > > > > @@ -1929,10 +1989,10 @@ char *flags_string(char *buf, char *end, void *flags_ptr, > > > > switch (fmt[1]) { > > > > case 'p': > > > > flags = *(unsigned long *)flags_ptr; > > > > - /* Remove zone id */ > > > > - flags &= (1UL << NR_PAGEFLAGS) - 1; > > > > names = pageflag_names; > > > > > > The "names" variable is needed only with "break;" when using the final > > > format_flags(buf, end, flags, names); > > > > > > > - break; > > > > + buf = format_flags(buf, end, flags & (BIT(NR_PAGEFLAGS) - 1), names); > > > > + buf = format_page_flags(buf, end, flags); > > > > > > I am sorry for my ignorance. I am not familiar with MM. > > > But it is pretty hard to understand what call does what. > > > > > > I have found the following comment in include/linux/page_flags.h: > > > > > > * The page flags field is split into two parts, the main flags area > > > * which extends from the low bits upwards, and the fields area which > > > * extends from the high bits downwards. > > > > > > Sigh, I know that you already reworked this several times because > > > people "nitpicked" about the code style. But it seems that it > > > rather diverged instead of converged. > > > > > > What about the following? > > > > > > Note: It is inpired by the names "main area" and "fields area" > > > mentioned in the above comment from page_flags.h. > > > I have later realized that "page_flags_layout" actually made > > > sense as well. Feel free to rename page_flags_fileds > > > back to page_flags_layout. > > > > > > Anyway, this is my proposal: > > > > > > > This proposal is similar to v2. > > I don't mind changing it back with your additional better naming. > > Great. > > > By the way, it will be better to make a little change per Joe's > > suggestion on v2 that using a pointer instead of the index, for > > example, > > > > for (p = pff; p < pff + ARRAY_SIZE(pff); p++) { > > This looks a bit non-standard. IMHO, Joe was not against using index. > He proposed: > > for (i = 0; i < ARRAY_SIZE(pfl) && buf < end; i++) { > > , see > https://lore.kernel.org/lkml/e5ea9e8b1190c2a397a1b84dd55bb9c706dc7058.camel@perches.com/ > > I am not sure about the (buf < end) check. It might be some > optimization or it did fit the the old code. > > Anyway, I like the currently used: > > for (i = 0; i < ARRAY_SIZE(pff); i++) { > > It is standard, easy to understand, and thus more safe. I am sure that > compiler will optimize it very well. > Fair enough, I will do it as you suggested in the next version. -- Thanks Yafang