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Shutemov" , Minchan Kim , Patrick Xia Content-Type: text/plain; charset="UTF-8" ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1664241886; a=rsa-sha256; cv=none; b=t1IexU+D+toaPB+dtu6rUrdHOjUTDl09OZr1Mw9T+5hAaP0kdyABOsENGacosZLTqiX/XN hsEFcIjTUoFJx8nof6A2qhi91w5lAEN4Q106Z6EYJ/1pOyjxUXdBkPLQ2Qr7ea53pogLB1 1COaa9yRoXAA1bhXwGtJdi30mhM9zB4= ARC-Authentication-Results: i=1; imf14.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=T98Ol14y; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf14.hostedemail.com: domain of zokeefe@google.com designates 209.85.167.177 as permitted sender) smtp.mailfrom=zokeefe@google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1664241886; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=x5/X7S0D0PsuMd9Bj3ADbJYnKoDs6aX3p9Vher7KPK4=; b=x385aybNnwG3rLVaQsAH9t7UH6dwUCWKyVyk0Wo0BZPEMln/6899SWBkeWdbjtyxn2lTDB 1588XiNCiaQsnLtmLF0uGaPI5fFQMlddBJOLOH8VtEfCDkIjDDtCUztpefx2iz7RP8aFvb DakY73v7Mx5X9sBo8o1Z94iZ1R3Nknw= X-Stat-Signature: tk7yh4zm8qtcsymwajg1nzi7hioq5k4i X-Rspam-User: X-Rspamd-Server: rspam04 Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=T98Ol14y; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf14.hostedemail.com: domain of zokeefe@google.com designates 209.85.167.177 as permitted sender) smtp.mailfrom=zokeefe@google.com X-Rspamd-Queue-Id: 9E710100004 X-HE-Tag: 1664241886-853540 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: > > +/* hpage must be locked, and mmap_lock must be held in write */ > > +static int set_huge_pmd(struct vm_area_struct *vma, unsigned long addr, > > + pmd_t *pmdp, struct page *hpage) > > +{ > > + struct vm_fault vmf = { > > + .vma = vma, > > + .address = addr, > > + .flags = 0, > > It means you are going to install a readonly PMD. It is fine for > readonly fs, but it may be not performant for shmem since the > following write will trigger wp fault then the PMD will be split. So > it should be ok to install writable PMD for shmem. > > But anyway this is not a fatal problem, the patch looks good to me. > Reviewed-by: Yang Shi > Thanks, Yang! I haven't worked out the details for writable shmem, but I'm hoping FAULT_FLAG_WRITE is enough here. I'm also now wondering if FAULT_FLAG_REMOTE is needed here for process_madvise(MADV_COLLAPSE) when called on behalf of another process; though that would also mean it's needed in __collapse_huge_page_swapin() as well (even when running as khugepaged). I can't say I fully understand 1b2ee1266ea6 ("mm/core: Do not enforce PKEY permissions on remote mm access"), but if the comment in include/linux/mm_types.h is to be trusted, then this would be the case.