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s=arc-20220608; d=hostedemail.com; t=1655714684; a=rsa-sha256; cv=none; b=jyGK33ZI/ZQkraBeDfS2iJvRaPYvExA9ie9JDa7Ao/eDOQwZSruiK6MlbbPaRTaLl6YGv1 SrrP7YYOldzt6jaSluuXMDNnLEeRces1aHDC2yJjrCUCsjT5EKnypLQND3FYFF2YjWgSgr euKYUVO7ezFYpWsEF5FfxoB5S/WEVsM= X-Rspamd-Queue-Id: 51FC41400AC Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=suse.de header.s=susede2_rsa header.b=lP9zx3xP; dkim=pass header.d=suse.de header.s=susede2_ed25519 header.b=OXh9d08J; dmarc=pass (policy=none) header.from=suse.de; spf=pass (imf26.hostedemail.com: domain of osalvador@suse.de designates 195.135.220.29 as permitted sender) smtp.mailfrom=osalvador@suse.de X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 77fgyeznohtmagj4hgo1hw56sq5rqoam X-HE-Tag: 1655714684-479452 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 Mon, Jun 20, 2022 at 04:29:11PM +0800, Muchun Song wrote: > > > Although it works, I think PageVmemmapSelfHosted() check for the 1st pfn's > > > vmemmap page is not always reliable. Since we reused PG_owner_priv_1 > > > as PG_vmemmap_self_hosted, the test is noly reliable for vmemmap page's > > > vmemmap page. Other non-vmemmap page can be flagged with PG_owner_priv_1. > > > So this check can be false-positive. Maybe the following code snippet is > > > the solution. > > > > How could that happen for pages used for backing a vmemmap? > > > > It cannot happen for memmap_on_memory case. Howwver, it can happen for other > cases. E.g. the 1st pfn (of boot memory block) whose vmemmap page may be flagged > as PG_owner_priv_1 (if PG_swapcache is set). Then, the check is false-positive. If this can really happen, which I am not that sure tbh, maybe a way out would be to just define a new page-type as we did in previous versions of memmap_on_memory. In that way we would not for flags, but for its type. But as I said, I am not entirely sure about the potential fallout of what you mention. -- Oscar Salvador SUSE Labs