From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 113587CF3F for ; Wed, 24 Jan 2024 18:40:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706121612; cv=none; b=PNxpiwI1yhQt0EWg5li/x2T5cFNlS1cJE4FBZgVAxRl/ffaL02ucSRFZjjR5HGoHsTiO3SOi4EHE3ahBSA1drvTCw3D2teAeOEYGhWIxBVs26OJY0lggHdPqSbJ7xFe75LsevC1P7NVjnWJWWorUD9bX1J8F8M7qXiQv9qwmrCo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706121612; c=relaxed/simple; bh=EMjjgo6EOUSHuhiIbOnLdaQNvcS1crAmIlcHC3Ptc8c=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=eeaZ8A7ILc7SPmYcT44bM2bWCB23p3OuXF8MmR+9SAg2veush0++viZjBIr/6lzL/ffbYtSy/aGTMo1ewpaw3GJxIXwotUkrPcyOyc9XvEXc4oH0BvSab+o7gMAfTDTYWC4mXmPKfO58pIXLiP2GJ5LlhVB4BxLKpnY9hPEJcmA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=g+zmg+Ym; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="g+zmg+Ym" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Transfer-Encoding: Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description; bh=draqL+CE/rP10cXaUi8xoo+aCaYER4SdwSjRFB4PIm8=; b=g+zmg+YmwmdzlghpYwJW/wat/t I/cEHh96j3CYzc1CTJqQpLR5HDfuqmoh7R+NZ42ScpDxaJF6gVLHWAL2nZchFm5v58pWmvbMeglcZ MzyF6Q2qAJeOzsmHNiGeTCRXXfqxTMW5L6tBKrwj5/B/oTA3UQ4ZS004KWeY9HEpm3HT5JyHChscz UFlgYfyno6PQR58/cQhX1glfFvyaelEpSFCbyIa0W8qR5M3QHKUwgZOhkm9A8xE9xMd05M/SaoN7s payZ5Eq73rquLSQmgMppR1ujBfIE5U0Xfucr3M/h90xU8t2SQfIvShi22ZeFYcHm+/0UNeBD9xqcB X3Zp449A==; Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1rSiAR-00000007SKc-2nnP; Wed, 24 Jan 2024 18:40:07 +0000 Date: Wed, 24 Jan 2024 18:40:07 +0000 From: Matthew Wilcox To: Haiqiang Gong =?utf-8?B?KOm+mua1t+W8uik=?= Cc: "linux-kernel@vger.kernel.org" , Mike Zhang =?utf-8?B?KOW8oOS8n+S8nyk=?= , Andrew Morton , Matthias Brugger , AngeloGioacchino Del Regno , "linux-mm@kvack.org" , "linux-arm-kernel@lists.infradead.org" , "linux-mediatek@lists.infradead.org" Subject: Re: =?utf-8?B?5Zue5aSNOiBbUEFUQ0g=?= =?utf-8?Q?=5D?= mm/compaction: add check mechanism to avoid cma alloc fail Message-ID: References: <20240122022317.30091-1-Haiqiang.Gong@mediatek.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Wed, Jan 24, 2024 at 07:20:53AM +0000, Haiqiang Gong (龚海强) wrote: > > I don't understand.  You say that the memory isn't movable, but then you > > say that it's migrated in.  So it was movable, but it's no longer > > movable after being moved once?  > Sorry for not expressing clearly > When doing memory migration, the kernel will determine whether the current > page can be moved based on the refcount and mapcount of the current page. > This memory can be moved during kernel compaction. At this time, refcount > is less than or equal to mapcount. > After this memory is kcompacted and placed in the cma buffer, under > certain special conditions, the refcount may be greater than the mapcount > （ex:the current page is being used by fs）, and then migrate will fail. But that's always true. Any page that is currently in use might have its refcount temporarily incremented. There's nothing special about pages that belong to a file. You've basically just prevented all filesystem memory from being migrated to the CMA area, and that's wrong. What's special about this page? Or were you just unlucky?