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[86.146.209.214]) by smtp.gmail.com with ESMTPSA id e18-20020a056000121200b002cf1c435afcsm5297568wrx.11.2023.03.15.12.04.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 Mar 2023 12:04:13 -0700 (PDT) Date: Wed, 15 Mar 2023 19:04:13 +0000 From: Lorenzo Stoakes To: Vlastimil Babka Cc: Andrew Morton , "Liam R. Howlett" , Matthew Wilcox , linux-mm@kvack.org, linux-kernel@vger.kernel.org, patches@lists.linux.dev, maple-tree@lists.infradead.org Subject: Re: [PATCH 02/10] mm/mmap/vma_merge: use the proper vma pointer in case 3 Message-ID: References: <20230309111258.24079-1-vbabka@suse.cz> <20230309111258.24079-3-vbabka@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230309111258.24079-3-vbabka@suse.cz> X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: i5euq6spphbauf8drmbdxc3aj774d881 X-Rspamd-Queue-Id: EA54F20013 X-HE-Tag: 1678907056-908848 X-HE-Meta: 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 +FSfU3pS TY+mhTxQgfLXE8xb6ET8wy3m/oXcRpC7cwxgVdK2U9sZ4bdzHF1puKTYlklwbGsJeqdtOWhuJmnF6/T0vOYUNHL2lywufJ7h+uZrgPGTXpNmno5Do+pMKxk5GlBPe3xowjtv/CyHi7vq3xKu8d6pju34hs2ByGN86hFPS51TqI8QS6M02CQrr28Gkia6bdbxBPHk4ItsV/RrM0DDEBvgtO8uwTa7lOjAGnGZpWkKzmMOn2tSMCAusRkf58ZNP+7meF7o3xCnyiTCTo89IGQBNFb+Vm2UYSxNpqPFBfCISEHX+ituHSv40cWlgShfxcnmXalI9AXBP9mSn2is++L7Y9seSDDZI2NXO6DntXNGF/gzyJVwtNZWXQh2+eRLcV6iztLBm+dKREk4Sm8+cJMkrXIWlaM5VQ+AR+AIOGrARkB6a6ojHBxCmEoPTmNmU8pIEPYMIFe/geVlc0UoUKWvKGFesrqYs5TjXtti6 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 Thu, Mar 09, 2023 at 12:12:50PM +0100, Vlastimil Babka wrote: > In case 3 we we use 'next' for everything but vma_pgoff. So use 'next' > for that as well, instead of 'mid', for consistency. Then in case 8 we > have to use 'mid' explicitly, which should also make the intent more > obvious. > > Adjust the diagram for cases 1-3 in the comment to match the code - we > are using 'next' for case 3 so mark the range with XXXX instead of NNNN. > For case 2 that's a no-op as the code doesn't touch 'next' or 'mid'. For > case 1 it's now wrong but that will be fixed next. > > No functional change. > > Signed-off-by: Vlastimil Babka > --- > mm/mmap.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > > diff --git a/mm/mmap.c b/mm/mmap.c > index 0a8b052e3022..1af4c9bc2c87 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -857,11 +857,11 @@ can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags, > * mmap, brk or case 4 below case 5 below > * mremap move: > * AAAA AAAA > - * PPPP NNNN PPPPNNNNXXXX > + * PPPP XXXX PPPPNNNNXXXX > * might become might become > * PPPPPPPPPPPP 1 or PPPPPPPPPPPP 6 or > - * PPPPPPPPNNNN 2 or PPPPPPPPXXXX 7 or > - * PPPPNNNNNNNN 3 PPPPXXXXXXXX 8 > + * PPPPPPPPXXXX 2 or PPPPPPPPXXXX 7 or > + * PPPPXXXXXXXX 3 PPPPXXXXXXXX 8 > * I'm glad you're making things more consistent and what you're addressing here is a real clanger, but these diagrams while great to have do definitely feel quite confusing even now. But that's something for a future patch! > * It is important for case 8 that the vma NNNN overlapping the > * region AAAA is never going to extended over XXXX. Instead XXXX must > @@ -978,9 +978,10 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, > vma = next; /* case 3 */ > vma_start = addr; > vma_end = next->vm_end; > - vma_pgoff = mid->vm_pgoff; > + vma_pgoff = next->vm_pgoff; > err = 0; > if (mid != next) { /* case 8 */ > + vma_pgoff = mid->vm_pgoff; > remove = mid; > err = dup_anon_vma(next, mid); > } > -- > 2.39.2 > This does fix a big incongruity in that previously everything but vm_pgoff was relative to next, while in the non-8 case mid is equal to next anyway. Good, clarifying improvement! Reviewed-by: Lorenzo Stoakes