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dkim=pass header.d=fb.com header.s=facebook header.b=NxtHln6m; spf=none (imf17.hostedemail.com: domain of "prvs=5109b6293c=songliubraving@fb.com" has no SPF policy when checking 67.231.145.42) smtp.mailfrom="prvs=5109b6293c=songliubraving@fb.com"; dmarc=pass (policy=reject) header.from=fb.com X-HE-Tag: 1650465794-376832 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 Linus, > On Apr 19, 2022, at 7:18 PM, Linus Torvalds wrote: >=20 > On Tue, Apr 19, 2022 at 7:03 PM Alexei Starovoitov > wrote: >>=20 >> Here is the quote from Song's cover letter for bpf_prog_pack series: >=20 > I care about performance as much as the next person, but I care about > correctness too. >=20 > That large-page code was a disaster, and was buggy and broken. >=20 > And even with those four patches, it's still broken. >=20 > End result: there's no way that thigh gets re-enabled without the > correctness being in place. >=20 > At a minimum, to re-enable it, it needs (a) that zeroing and (b) > actual numbers on real loads. (not some artificial benchmark). >=20 > Because without (a) there's no way in hell I'll enable it. >=20 > And without (b), "performance" isn't actually an argument. I will send patch to do (a) later this week.=20 For (b), we have seen direct map fragmentation causing visible performance drop for our major services. This is the shadow=20 production benchmark, so it is not possible to run it out of=20 our data centers. Tracing showed that BPF program was the top=20 trigger of these direct map splits.=20 Thanks, Song=