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Wed, 31 Jul 2024 10:18:07 +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 4dcSMl8PqmZxKQAAD6G6ig (envelope-from ); Wed, 31 Jul 2024 10:18:07 +0000 Message-ID: Date: Wed, 31 Jul 2024 12:18:07 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/4] mm: Document __GFP_NOFAIL must be blockable Content-Language: en-US To: Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org Cc: 42.hyeyoo@gmail.com, cl@linux.com, hailong.liu@oppo.com, hch@infradead.org, iamjoonsoo.kim@lge.com, lstoakes@gmail.com, mhocko@suse.com, penberg@kernel.org, rientjes@google.com, roman.gushchin@linux.dev, torvalds@linux-foundation.org, urezki@gmail.com, v-songbaohua@oppo.com, virtualization@lists.linux.dev References: <20240731000155.109583-1-21cnbao@gmail.com> <20240731000155.109583-3-21cnbao@gmail.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: <20240731000155.109583-3-21cnbao@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: BDB134002B X-Stat-Signature: uzjk7c9e778y51749nktsb5ioigdqap4 X-HE-Tag: 1722421089-689638 X-HE-Meta: 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 h0dfwpau 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 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 7/31/24 2:01 AM, Barry Song wrote: > From: Barry Song > > Non-blocking allocation with __GFP_NOFAIL is not supported and may > still result in NULL pointers (if we don't return NULL, we result > in busy-loop within non-sleepable contexts): > > static inline struct page * > __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > struct alloc_context *ac) > { > ... > /* > * Make sure that __GFP_NOFAIL request doesn't leak out and make sure > * we always retry > */ > if (gfp_mask & __GFP_NOFAIL) { > /* > * All existing users of the __GFP_NOFAIL are blockable, so warn > * of any new users that actually require GFP_NOWAIT > */ > if (WARN_ON_ONCE_GFP(!can_direct_reclaim, gfp_mask)) > goto fail; > ... > } > ... > fail: > warn_alloc(gfp_mask, ac->nodemask, > "page allocation failure: order:%u", order); > got_pg: > return page; > } > > Highlight this in the documentation of __GFP_NOFAIL so that non-mm > subsystems can reject any illegal usage of __GFP_NOFAIL with > GFP_ATOMIC, GFP_NOWAIT, etc. > > Acked-by: Michal Hocko > Signed-off-by: Barry Song Acked-by: Vlastimil Babka > --- > include/linux/gfp_types.h | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/include/linux/gfp_types.h b/include/linux/gfp_types.h > index 313be4ad79fd..4a1fa7706b0c 100644 > --- a/include/linux/gfp_types.h > +++ b/include/linux/gfp_types.h > @@ -215,7 +215,8 @@ enum { > * the caller still has to check for failures) while costly requests try to be > * not disruptive and back off even without invoking the OOM killer. > * The following three modifiers might be used to override some of these > - * implicit rules. > + * implicit rules. Please note that all of them must be used along with > + * %__GFP_DIRECT_RECLAIM flag. > * > * %__GFP_NORETRY: The VM implementation will try only very lightweight > * memory direct reclaim to get some memory under memory pressure (thus > @@ -246,6 +247,8 @@ enum { > * cannot handle allocation failures. The allocation could block > * indefinitely but will never return with failure. Testing for > * failure is pointless. > + * It _must_ be blockable and used together with __GFP_DIRECT_RECLAIM. > + * It should _never_ be used in non-sleepable contexts. So this second line is a bit redundant as you can't use __GFP_DIRECT_RECLAIM in non-sleepable contexts. But can't hurt so not a objection. > * New users should be evaluated carefully (and the flag should be > * used only when there is no reasonable failure policy) but it is > * definitely preferable to use the flag rather than opencode endless