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Fri, 19 Jul 2024 10:19:47 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id X177DMM9mmaJVgAAD6G6ig (envelope-from ); Fri, 19 Jul 2024 10:19:47 +0000 Message-ID: <5c9f852f-f00b-4543-830b-7dd71d5042e0@suse.cz> Date: Fri, 19 Jul 2024 12:19:46 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 1/3] memcontrol: define root_mem_cgroup for CONFIG_MEMCG=n cases Content-Language: en-US To: Qu Wenruo , linux-btrfs@vger.kernel.org Cc: hannes@cmpxchg.org, mhocko@kernel.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, cgroups@vger.kernel.org, linux-mm@kvack.org References: <299298648bc5689b2f163c7876936179338301ba.1721380449.git.wqu@suse.com> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJkBREIBQkRadznAAoJECJPp+fMgqZkNxIQ ALZRqwdUGzqL2aeSavbum/VF/+td+nZfuH0xeWiO2w8mG0+nPd5j9ujYeHcUP1edE7uQrjOC Gs9sm8+W1xYnbClMJTsXiAV88D2btFUdU1mCXURAL9wWZ8Jsmz5ZH2V6AUszvNezsS/VIT87 AmTtj31TLDGwdxaZTSYLwAOOOtyqafOEq+gJB30RxTRE3h3G1zpO7OM9K6ysLdAlwAGYWgJJ V4JqGsQ/lyEtxxFpUCjb5Pztp7cQxhlkil0oBYHkudiG8j1U3DG8iC6rnB4yJaLphKx57NuQ PIY0Bccg+r9gIQ4XeSK2PQhdXdy3UWBr913ZQ9AI2usid3s5vabo4iBvpJNFLgUmxFnr73SJ KsRh/2OBsg1XXF/wRQGBO9vRuJUAbnaIVcmGOUogdBVS9Sun/Sy4GNA++KtFZK95U7J417/J Hub2xV6Ehc7UGW6fIvIQmzJ3zaTEfuriU1P8ayfddrAgZb25JnOW7L1zdYL8rXiezOyYZ8Fm ZyXjzWdO0RpxcUEp6GsJr11Bc4F3aae9OZtwtLL/jxc7y6pUugB00PodgnQ6CMcfR/HjXlae h2VS3zl9+tQWHu6s1R58t5BuMS2FNA58wU/IazImc/ZQA+slDBfhRDGYlExjg19UXWe/gMcl De3P1kxYPgZdGE2eZpRLIbt+rYnqQKy8UxlszsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZAUSmwUJDK5EZgAKCRAiT6fnzIKmZOJGEACOKABgo9wJXsbWhGWYO7mD 8R8mUyJHqbvaz+yTLnvRwfe/VwafFfDMx5GYVYzMY9TWpA8psFTKTUIIQmx2scYsRBUwm5VI EurRWKqENcDRjyo+ol59j0FViYysjQQeobXBDDE31t5SBg++veI6tXfpco/UiKEsDswL1WAr tEAZaruo7254TyH+gydURl2wJuzo/aZ7Y7PpqaODbYv727Dvm5eX64HCyyAH0s6sOCyGF5/p eIhrOn24oBf67KtdAN3H9JoFNUVTYJc1VJU3R1JtVdgwEdr+NEciEfYl0O19VpLE/PZxP4wX PWnhf5WjdoNI1Xec+RcJ5p/pSel0jnvBX8L2cmniYnmI883NhtGZsEWj++wyKiS4NranDFlA HdDM3b4lUth1pTtABKQ1YuTvehj7EfoWD3bv9kuGZGPrAeFNiHPdOT7DaXKeHpW9homgtBxj 8aX/UkSvEGJKUEbFL9cVa5tzyialGkSiZJNkWgeHe+jEcfRT6pJZOJidSCdzvJpbdJmm+eED w9XOLH1IIWh7RURU7G1iOfEfmImFeC3cbbS73LQEFGe1urxvIH5K/7vX+FkNcr9ujwWuPE9b 1C2o4i/yZPLXIVy387EjA6GZMqvQUFuSTs/GeBcv0NjIQi8867H3uLjz+mQy63fAitsDwLmR EP+ylKVEKb0Q2A== In-Reply-To: <299298648bc5689b2f163c7876936179338301ba.1721380449.git.wqu@suse.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: mbuqc8jcqy1hfozsenqrgbicgyum7m9e X-Rspam-User: X-Rspamd-Queue-Id: D83C04002D X-Rspamd-Server: rspam02 X-HE-Tag: 1721384388-385998 X-HE-Meta: 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 /RcVEbiv h2Ugp8X/AATCjBmFJZylzeUZGBb7VKTBuIobndMpZv+z/Hc0YkgtPUc0KQfu7uq0r2p0m7xiK6Mtpa7MlJFmsrA7RVLyddAQXaW5rMFu5hDDFPzQq1c8z5WNiIAQbSlZOceVJ9n/cE0bXdwZWHHF2Sh577dEchtMAZr3aZNOnxpjSK4sMQQhzNfDpaDUZ8ppjo4tRg9LZPI5BeFcmNOXR9+vcUaia2ZPBEC0+/I7skokzGm8YkBBKwii5RqPbGbYvfWfOk5L55zUxz13fzJOmJ3oeRSMJcJcZpHKiPgrK/RDoGcnooGvIiygjJ9jS7hrpDmdlxoRMEzjPWaQNz0efQIEVakl+4tKdBD/QBwI+KjB7dps= 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 7/19/24 11:16 AM, Qu Wenruo wrote: > There is an incoming btrfs patchset, which will use @root_mem_cgroup as > the active cgroup to attach metadata folios to its internal btree > inode, so that btrfs can skip the possibly costly charge for the > internal inode which is only accessible by btrfs itself. > > However @root_mem_cgroup is not always defined (not defined for > CONFIG_MEMCG=n case), thus all such callers need to do the extra > handling for different CONFIG_MEMCG settings. > > So here we add a special macro definition of root_mem_cgroup, making it > to always be NULL. > > The advantage of this, other than pulling the pointer definition out, > is that we will avoid wasting global data section space for such > pointer. > > Signed-off-by: Qu Wenruo > --- > include/linux/memcontrol.h | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index 030d34e9d117..a268585babdc 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -329,8 +329,6 @@ struct mem_cgroup { > */ > #define MEMCG_CHARGE_BATCH 64U > > -extern struct mem_cgroup *root_mem_cgroup; > - This breaks the CONFIG_MEMCG=y case? > enum page_memcg_data_flags { > /* page->memcg_data is a pointer to an slabobj_ext vector */ > MEMCG_DATA_OBJEXTS = (1UL << 0), > @@ -346,6 +344,12 @@ enum page_memcg_data_flags { > > #define __FIRST_OBJEXT_FLAG (1UL << 0) > > +/* > + * For CONFIG_MEMCG=n case, still define a root_mem_cgroup, but that will > + * always be NULL and not taking any global data section space. > + */ > +#define root_mem_cgroup (NULL) > + > #endif /* CONFIG_MEMCG */ > > enum objext_flags {