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bh=MZNUwnLOsEGSk31jY/DD7SZRIPUoW6IOu2ayBkyBwbE=; b=oel62jizuTQv+SEdGMN1wmChnapG/RR8rfFZ4XS/uCUBLan6uE/qNdeleiPqKRqtF0te/d n9nZTQ7gT+E7O5mSD/GhZBf8wG7pvWhusvKamV1jiiovQlO7K1atrXybHMvsU6xi7KgsNb XnWdwIADQjbFFgp8Ke3XlX2pRQnI+Fk= X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 4113640012 X-Stat-Signature: jd987c3smyi39s1wyjtieotzbesbghhf Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=fb.com header.s=facebook header.b=SMMpFjmk; dmarc=pass (policy=reject) header.from=fb.com; arc=pass ("microsoft.com:s=arcselector9901:i=1"); spf=pass (imf12.hostedemail.com: domain of "prvs=9235dc5586=songliubraving@fb.com" designates 67.231.153.30 as permitted sender) smtp.mailfrom="prvs=9235dc5586=songliubraving@fb.com" X-Rspam-User: X-HE-Tag: 1661360853-934190 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: Hi Peter,=20 > On Aug 22, 2022, at 9:56 AM, Song Liu wrote: >=20 >> On Aug 22, 2022, at 9:34 AM, Peter Zijlstra wrote= : >>=20 >> On Mon, Aug 22, 2022 at 03:46:38PM +0000, Song Liu wrote: >>> Could you please share your feedback on this?=20 >>=20 >> I've looked at it all of 5 minutes, so perhaps I've missed something. >>=20 >> However, I'm a little surprised you went with a second tree instead of >> doing the top-down thing for data. The way you did it makes it hard to >> have guard pages between text and data. >=20 > I didn't realize the importance of the guard pages. But it is not too > hard to do it with this approach. For each 2MB text page, we can reserve > 4kB on the beginning and end of it. Would this work? >=20 > There are a couple benefits from a second tree: >=20 > 1. It allows text allocations to go below PAGE_SIZE granularity, while=20 > data allocations would still use PAGE_SIZE granularity, which is the > same as current code.=20 > 2. Text allocate requires mapping one vm_struct to many vmap_area. Puttin= g > text allocations in a separate tree make it easier to handle this.=20 > (Well, I haven't finished this logic yet).=20 > 3. A separate tree makes it easier to use text tail page,=20 > [_etext, roundup(_etext, PMD_SIZE)], for modules and BPF programs.=20 >=20 > Does this make sense? Do you see other downsides with a second tree? Did these make sense? Do you have future comments that I would address in=20 future versions? Thanks, Song