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Fri, 25 Oct 2024 17:35:22 +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 pWrlLNrWG2c2FwAAD6G6ig (envelope-from ); Fri, 25 Oct 2024 17:35:22 +0000 Message-ID: <21e7bed9-b705-4fb1-84e6-9fab2e66dbeb@suse.cz> Date: Fri, 25 Oct 2024 19:35:22 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 4/5] mm: remove unnecessary reset state logic on merge new VMA Content-Language: en-US To: Lorenzo Stoakes , Andrew Morton Cc: "Liam R . Howlett" , Jann Horn , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Linus Torvalds , Peter Xu References: <5d9a59eee6498ae017cc87d89aa723de7179f75d.1729858176.git.lorenzo.stoakes@oracle.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: <5d9a59eee6498ae017cc87d89aa723de7179f75d.1729858176.git.lorenzo.stoakes@oracle.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: 8k6mzaff67tkfdsuffeh9up4wdh8o6r9 X-Rspamd-Queue-Id: 561EF10000F X-Rspamd-Server: rspam02 X-HE-Tag: 1729877702-844253 X-HE-Meta: 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 XAZQMshX DH3wB5atvLgx1mrm772mZEYZnhF5HfClpBkupFqGeX5IS2d6iiIlZDrqi9i/VF7oWgz8ewZjvC20mR0d4WoPs8Cf8ZEwabNefNBobhs6t8C+1FoCCrqnfqr2EBn38ILRebMRuJPxJ2sXCcQmr8WUTTnLn8noPKx1dxkKPGUahqHINYLvXKh+a9rl45qDTSMBtopv2mNW9+tMZR8ePvgQ9sIMagWUF8AICoAx1kFWLN1E8eU17SsTVa6YLdSeUnr4MgmLoa2JZOfbZatNw+8vE+hsi7i1DB96f162rRnS5zMlZ7gY93cdGzLLOOQ== 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 10/25/24 14:26, Lorenzo Stoakes wrote: > The only place where this was used was in mmap_region(), which we have now > adjusted to not require this to be performed (we reset ourselves in > effect). > > It also created a dangerous assumption that VMG state could be safely > reused after a merge, at which point it may have been mutated in unexpected > ways, leading to subtle bugs. > > Note that it was discovered by Wei Yang that there was also an error in > this code - we are comparing vmg->vma with prev after setting it to > NULL. > > This however had no impact, as we previously reset VMA iterator state > before attempting merge again, but it was useless effort. > > In any case, this patch removes all of the logic so also eliminates this > wasted effort. > > Signed-off-by: Lorenzo Stoakes Yeah glad to be rid of this. Reviewed-by: Vlastimil Babka > --- > mm/vma.c | 11 ----------- > 1 file changed, 11 deletions(-) > > diff --git a/mm/vma.c b/mm/vma.c > index b91c947babd6..7c690be67910 100644 > --- a/mm/vma.c > +++ b/mm/vma.c > @@ -963,7 +963,6 @@ struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg) > struct vm_area_struct *next = vmg->next; > unsigned long start = vmg->start; > unsigned long end = vmg->end; > - pgoff_t pgoff = vmg->pgoff; > pgoff_t pglen = PHYS_PFN(end - start); > bool can_merge_left, can_merge_right; > bool just_expand = vmg->merge_flags & VMG_FLAG_JUST_EXPAND; > @@ -1020,16 +1019,6 @@ struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg) > return vmg->vma; > } > > - /* If expansion failed, reset state. Allows us to retry merge later. */ > - if (!just_expand) { > - vmg->vma = NULL; > - vmg->start = start; > - vmg->end = end; > - vmg->pgoff = pgoff; > - if (vmg->vma == prev) > - vma_iter_set(vmg->vmi, start); > - } > - > return NULL; > } >