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Fri, 25 Oct 2024 09:43:20 +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 8s9ZIjhoG2ezewAAD6G6ig (envelope-from ); Fri, 25 Oct 2024 09:43:20 +0000 Message-ID: <2ca9450c-b5aa-4e7d-aa7b-437d9aec45dd@suse.cz> Date: Fri, 25 Oct 2024 11:43:20 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 8/8] mm: defer second attempt at merge on mmap() 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: 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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Level: X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-0.999]; MIME_GOOD(-0.10)[text/plain]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCPT_COUNT_SEVEN(0.00)[8]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[oracle.com:email,imap1.dmz-prg2.suse.org:helo] X-Spam-Score: -4.30 X-Spam-Flag: NO On 10/23/24 22:38, Lorenzo Stoakes wrote: > Rather than trying to merge again when ostensibly allocating a new VMA, > instead defer until the VMA is added and attempt to merge the existing > range. > > This way we have no complicated unwinding logic midway through the process > of mapping the VMA. > > In addition this removes limitations on the VMA not being able to be the > first in the virtual memory address space which was previously implicitly > required. > > It also performs this merge after the final flag adjustments are performed, > something that was not done previously and thus might have prevented > possibly valid merges in the past. > > In theory, for this very same reason, we should unconditionally attempt > merge here, however this is likely to have a performance impact so it is > better to avoid this given the unlikely outcome of a merge. Maybe just expand the cases where we set map->retry_merge, i.e. in case the final flag adjustments do anything? > The vmg state will already have been reset by the first attempt at a merge > so we only need to reset the iterator, set the vma and flags and try again. > > Signed-off-by: Lorenzo Stoakes Reviewed-by: Vlastimil Babka A nit: > --- > mm/vma.c | 75 ++++++++++++++++++++------------------------------------ > 1 file changed, 26 insertions(+), 49 deletions(-) > > diff --git a/mm/vma.c b/mm/vma.c > index 065f5e1f65be..c493ecebf394 100644 > --- a/mm/vma.c > +++ b/mm/vma.c > @@ -19,6 +19,7 @@ struct mmap_state { > struct file *file; > > unsigned long charged; > + bool retry_merge; > > struct vm_area_struct *prev; > struct vm_area_struct *next; > @@ -2280,9 +2281,9 @@ static int __mmap_prepare(struct mmap_state *map, struct vma_merge_struct *vmg, > return 0; > } > > + > static int __mmap_new_file_vma(struct mmap_state *map, > - struct vma_merge_struct *vmg, > - struct vm_area_struct **vmap, bool *mergedp) > + struct vm_area_struct **vmap) > { > struct vma_iterator *vmi = map->vmi; > struct vm_area_struct *vma = *vmap; > @@ -2311,37 +2312,11 @@ static int __mmap_new_file_vma(struct mmap_state *map, > !(map->flags & VM_MAYWRITE) && > (vma->vm_flags & VM_MAYWRITE)); > > - vma_iter_config(vmi, map->addr, map->end); > - /* > - * If flags changed after mmap_file(), we should try merge > - * vma again as we may succeed this time. > - */ > - if (unlikely(map->flags != vma->vm_flags && map->prev)) { > - struct vm_area_struct *merge; > - > - vmg->flags = vma->vm_flags; > - /* If this fails, state is reset ready for a reattempt. */ > - merge = vma_merge_new_range(vmg); > - > - if (merge) { > - /* > - * ->mmap() can change vma->vm_file and fput > - * the original file. So fput the vma->vm_file > - * here or we would add an extra fput for file > - * and cause general protection fault > - * ultimately. > - */ > - fput(vma->vm_file); > - vm_area_free(vma); > - vma = merge; > - *mergedp = true; > - } else { > - vma_iter_config(vmi, map->addr, map->end); > - } > - } > + /* If the flags change (and are mergeable), let's retry later. */ > + map->retry_merge = vma->vm_flags != map->flags && !(vma->vm_flags & VM_SPECIAL); > > + vma_iter_config(vmi, map->addr, map->end); Do we need this still? __mmap_new_vma() did that and nothing changed since in the non-error case, AFAICS? > map->flags = vma->vm_flags; > - *vmap = vma; > return 0; > } >