From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mout.gmx.net (mout.gmx.net [212.227.15.15]) (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 C55B63A267; Thu, 12 Sep 2024 01:45:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=212.227.15.15 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726105553; cv=none; b=E8bzpmB09C5t/5eW4oNTk8CippipSG9RRZ12DiXmoeENNxm2xHpl4A+ZJJeymU6NRHy6tY7I/CeogU/zatERWggQ1RBQ75P0u2EQmwN1ElskNdKa/v6A1XP7kIV4JPCIF7SNPRHVTfF+ORlizkNthhT5o7ku7uk7mhMRtGXITdc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726105553; c=relaxed/simple; bh=2QSGq7Hd1MMLyuiC5BTYhqH45996ucGyyGvy2UiO6+I=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=C0+QaxMnJiU3p46kXR37pSKwNWSNfx87l1b0dLHFQqqEWTgzdHUdoBd75wWrIfHIxcrARrWEVesIBQUH2Iqif5+ni/SnPqkw/YNkO+VibY/DdQ0Q5/vyd4xfpLqy2Y3+Wnk0wvxHeiPo8WAhnwaZhUpHULPQLsKAIHK6So8C8ng= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=gmx.de; spf=pass smtp.mailfrom=gmx.de; dkim=pass (2048-bit key) header.d=gmx.de header.i=deller@gmx.de header.b=qjO3GeyN; arc=none smtp.client-ip=212.227.15.15 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=gmx.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmx.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmx.de header.i=deller@gmx.de header.b="qjO3GeyN" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmx.de; s=s31663417; t=1726105535; x=1726710335; i=deller@gmx.de; bh=9S8ZYir8xrchk1sw1I6nlFiM6OfsAfPDqkCmx/PX2JQ=; h=X-UI-Sender-Class:Message-ID:Date:MIME-Version:Subject:To:Cc: References:From:In-Reply-To:Content-Type: Content-Transfer-Encoding:cc:content-transfer-encoding: content-type:date:from:message-id:mime-version:reply-to:subject: to; b=qjO3GeyNRw8HljolMA/yl7sWFDBBbdDgSC3aUmelZJ+ZeiLXKfJuVejybrxmJGfF EvsOMnjB1brxT9/AQuey61bsWEvxd5Ey9HoikBnu3rNdc6M8Bp/LTbj7HK8RxGw1A 1TaLE1zjl8TP4p1GP6tgtOlt6dWk58CbMpnutjaK8IAgxQPac9IqtOg7rXHGa6v8y R7MnSuw8Eks65CqqiLSRPJ2NONwUF6HvASfQ0MWBIaeEvikT9nltAF59DGVhbvdfD WgRjPY4PbLUGHRIQL5S1LDXfW+bWoyaD9X7QXdYI8VVFKXFnwzGVMdX/1o3MAuRQv KsppuEclNv6ak54G7Q== X-UI-Sender-Class: 724b4f7f-cbec-4199-ad4e-598c01a50d3a Received: from [192.168.20.55] ([109.250.63.79]) by mail.gmx.net (mrgmx005 [212.227.17.190]) with ESMTPSA (Nemesis) id 1MbRfv-1sHz2E16d7-00iCe3; Thu, 12 Sep 2024 03:45:35 +0200 Message-ID: Date: Thu, 12 Sep 2024 03:45:33 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] [RFC] mm: mmap: Allow mmap(MAP_STACK) to map growable stack To: Yang Shi Cc: "Liam R. Howlett" , Helge Deller , linux-kernel@vger.kernel.org, Andrew Morton , linux-mm@kvack.org, linux-parisc@vger.kernel.org References: <95c4efe9-e92a-46fe-bf41-9141e125332d@gmx.de> Content-Language: en-US From: Helge Deller Autocrypt: addr=deller@gmx.de; keydata= xsFNBF3Ia3MBEAD3nmWzMgQByYAWnb9cNqspnkb2GLVKzhoH2QD4eRpyDLA/3smlClbeKkWT HLnjgkbPFDmcmCz5V0Wv1mKYRClAHPCIBIJgyICqqUZo2qGmKstUx3pFAiztlXBANpRECgwJ r+8w6mkccOM9GhoPU0vMaD/UVJcJQzvrxVHO8EHS36aUkjKd6cOpdVbCt3qx8cEhCmaFEO6u CL+k5AZQoABbFQEBocZE1/lSYzaHkcHrjn4cQjc3CffXnUVYwlo8EYOtAHgMDC39s9a7S90L 69l6G73lYBD/Br5lnDPlG6dKfGFZZpQ1h8/x+Qz366Ojfq9MuuRJg7ZQpe6foiOtqwKym/zV dVvSdOOc5sHSpfwu5+BVAAyBd6hw4NddlAQUjHSRs3zJ9OfrEx2d3mIfXZ7+pMhZ7qX0Axlq Lq+B5cfLpzkPAgKn11tfXFxP+hcPHIts0bnDz4EEp+HraW+oRCH2m57Y9zhcJTOJaLw4YpTY GRUlF076vZ2Hz/xMEvIJddRGId7UXZgH9a32NDf+BUjWEZvFt1wFSW1r7zb7oGCwZMy2LI/G aHQv/N0NeFMd28z+deyxd0k1CGefHJuJcOJDVtcE1rGQ43aDhWSpXvXKDj42vFD2We6uIo9D 1VNre2+uAxFzqqf026H6cH8hin9Vnx7p3uq3Dka/Y/qmRFnKVQARAQABzRxIZWxnZSBEZWxs ZXIgPGRlbGxlckBnbXguZGU+wsGRBBMBCAA7AhsDBQsJCAcCBhUKCQgLAgQWAgMBAh4BAheA FiEERUSCKCzZENvvPSX4Pl89BKeiRgMFAl3J1zsCGQEACgkQPl89BKeiRgNK7xAAg6kJTPje uBm9PJTUxXaoaLJFXbYdSPfXhqX/BI9Xi2VzhwC2nSmizdFbeobQBTtRIz5LPhjk95t11q0s uP5htzNISPpwxiYZGKrNnXfcPlziI2bUtlz4ke34cLK6MIl1kbS0/kJBxhiXyvyTWk2JmkMi REjR84lCMAoJd1OM9XGFOg94BT5aLlEKFcld9qj7B4UFpma8RbRUpUWdo0omAEgrnhaKJwV8 qt0ULaF/kyP5qbI8iA2PAvIjq73dA4LNKdMFPG7Rw8yITQ1Vi0DlDgDT2RLvKxEQC0o3C6O4 iQq7qamsThLK0JSDRdLDnq6Phv+Yahd7sDMYuk3gIdoyczRkXzncWAYq7XTWl7nZYBVXG1D8 gkdclsnHzEKpTQIzn/rGyZshsjL4pxVUIpw/vdfx8oNRLKj7iduf11g2kFP71e9v2PP94ik3 Xi9oszP+fP770J0B8QM8w745BrcQm41SsILjArK+5mMHrYhM4ZFN7aipK3UXDNs3vjN+t0zi qErzlrxXtsX4J6nqjs/mF9frVkpv7OTAzj7pjFHv0Bu8pRm4AyW6Y5/H6jOup6nkJdP/AFDu 5ImdlA0jhr3iLk9s9WnjBUHyMYu+HD7qR3yhX6uWxg2oB2FWVMRLXbPEt2hRGq09rVQS7DBy dbZgPwou7pD8MTfQhGmDJFKm2jvOwU0EXchrcwEQAOsDQjdtPeaRt8EP2pc8tG+g9eiiX9Sh rX87SLSeKF6uHpEJ3VbhafIU6A7hy7RcIJnQz0hEUdXjH774B8YD3JKnAtfAyuIU2/rOGa/v UN4BY6U6TVIOv9piVQByBthGQh4YHhePSKtPzK9Pv/6rd8H3IWnJK/dXiUDQllkedrENXrZp eLUjhyp94ooo9XqRl44YqlsrSUh+BzW7wqwfmu26UjmAzIZYVCPCq5IjD96QrhLf6naY6En3 ++tqCAWPkqKvWfRdXPOz4GK08uhcBp3jZHTVkcbo5qahVpv8Y8mzOvSIAxnIjb+cklVxjyY9 dVlrhfKiK5L+zA2fWUreVBqLs1SjfHm5OGuQ2qqzVcMYJGH/uisJn22VXB1c48yYyGv2HUN5 lC1JHQUV9734I5cczA2Gfo27nTHy3zANj4hy+s/q1adzvn7hMokU7OehwKrNXafFfwWVK3OG 1dSjWtgIv5KJi1XZk5TV6JlPZSqj4D8pUwIx3KSp0cD7xTEZATRfc47Yc+cyKcXG034tNEAc xZNTR1kMi9njdxc1wzM9T6pspTtA0vuD3ee94Dg+nDrH1As24uwfFLguiILPzpl0kLaPYYgB wumlL2nGcB6RVRRFMiAS5uOTEk+sJ/tRiQwO3K8vmaECaNJRfJC7weH+jww1Dzo0f1TP6rUa fTBRABEBAAHCwXYEGAEIACAWIQRFRIIoLNkQ2+89Jfg+Xz0Ep6JGAwUCXchrcwIbDAAKCRA+ Xz0Ep6JGAxtdEAC54NQMBwjUNqBNCMsh6WrwQwbg9tkJw718QHPw43gKFSxFIYzdBzD/YMPH l+2fFiefvmI4uNDjlyCITGSM+T6b8cA7YAKvZhzJyJSS7pRzsIKGjhk7zADL1+PJei9p9idy RbmFKo0dAL+ac0t/EZULHGPuIiavWLgwYLVoUEBwz86ZtEtVmDmEsj8ryWw75ZIarNDhV74s BdM2ffUJk3+vWe25BPcJiaZkTuFt+xt2CdbvpZv3IPrEkp9GAKof2hHdFCRKMtgxBo8Kao6p Ws/Vv68FusAi94ySuZT3fp1xGWWf5+1jX4ylC//w0Rj85QihTpA2MylORUNFvH0MRJx4mlFk XN6G+5jIIJhG46LUucQ28+VyEDNcGL3tarnkw8ngEhAbnvMJ2RTx8vGh7PssKaGzAUmNNZiG MB4mPKqvDZ02j1wp7vthQcOEg08z1+XHXb8ZZKST7yTVa5P89JymGE8CBGdQaAXnqYK3/yWf FwRDcGV6nxanxZGKEkSHHOm8jHwvQWvPP73pvuPBEPtKGLzbgd7OOcGZWtq2hNC6cRtsRdDx 4TAGMCz4j238m+2mdbdhRh3iBnWT5yPFfnv/2IjFAk+sdix1Mrr+LIDF++kiekeq0yUpDdc4 ExBy2xf6dd+tuFFBp3/VDN4U0UfG4QJ2fg19zE5Z8dS4jGIbLg== In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable X-Provags-ID: V03:K1:B/Ce3BWOxRWAzlUCr6qoViDtODHFPqm9ZzOjouNnMpYvXYkqXlG aQw4KdX//Y8/TobOETNoR7ZhJ42mCfJxUuS/RsTsjh1ISoLbC47LU0p5dDGcaz0XnztIh+G emEVb08RRtPRS/YVFpBiliNd2q34aED3Q4wtjLYNvjGU8vVTtdvAfBAiZFdNmUk2zBIHY3x GH5We/fXz3YNs0FTFxoxw== X-Spam-Flag: NO UI-OutboundReport: notjunk:1;M01:P0:6NRbv/9xRcM=;3n4A+SmKFN6NsO7EqZOWEj1Qv0F QdbXBS5tDYsik2Lr5MXFIpcm1ZhGyypNu1U83bFOxmBDEpAklYFW6YLwJmkcXGv7skHaivLtl l+NzJmgIhvSK+ZReX9ITRQ1Ty2taCwlS1YR3Q4qfAfhJe6ARWlVuntfpEZoIfhb+iKhPJVzxQ rXyyt+gBsTuRPa3YlO5C3jMjBb34AtEv41rpT1DSIWiPgTIeDlxKPPX7cU8X0FoIr7IXYeDwj 6LP3GPov/rknsmqj0IDqIlCw13YCbYASRWfGrFoQ06EBYUsqulZdTssZ0kHtk2jqB9YQznZsX oI/3TkzNGvH5OXBRxqvBJEw6HtlOrCjUr7Py+9+9mUyUp7HTfy0vuE6PEbu5w/3PpZnxg6oan VFzi2UOYIMkAuDL86jgTMR5SIVn3oR6EHsFrJo0KAubaASsDIrUR3iq9ho61Ijq/FfJu1WdyP 4KBVDosNg0ZS9RtLdar08+5KWkB3bNkWJikSMa02LNmlB3eAEsHWQMvf0ZKj8igEi4L0DSZgi plvQ09GHOMAwwffax7rf6qqJcwhCP9SqDbNnbkY16ywOqK8NtMEzJAUxP3c9KK3KRypakssPB nkgjNcHaCPxMkLCmgqdX0IMbBBQqrooxkWOiw4yZgwofzu+Q6B++UP1uNFWy6r/9xJdPhtPKG Q/M7aB6aTu4si6slQlMUFK4nMqtvv2jNNIDCwPIpaU//gDArsVr22oaErasIk4NDZwE77k1XV C/jU6xLGTA0HFARQxhJAAOhsiwo4qbZjcy2VzA+68iCeHhzdSPbhcgGXrOcloaD6ZWaDycUqO p+WhxhD5zIIbHJM0EO+1xw0Q== On 9/12/24 03:08, Yang Shi wrote: > On Wed, Sep 11, 2024 at 5:50=E2=80=AFPM Helge Deller wro= te: >> >> On 9/12/24 01:05, Liam R. Howlett wrote: >>> * Yang Shi [240911 18:16]: >>>> On Wed, Sep 11, 2024 at 12:49=E2=80=AFPM Liam R. Howlett >>>> wrote: >>>>> >>>>> * Helge Deller [240911 15:20]: >>>>>> This is a RFC to change the behaviour of mmap(MAP_STACK) to be >>>>>> sufficient to map memory for usage as stack on all architectures. >>>>>> Currently MAP_STACK is a no-op on Linux, and instead MAP_GROWSDOWN >>>>>> has to be used. >>>>>> To clarify, here is the relevant info from the mmap() man page: >>>>>> >>>>>> MAP_GROWSDOWN >>>>>> This flag is used for stacks. It indicates to the kernel virtu= al >>>>>> memory system that the mapping should extend downward in memor= y. The >>>>>> return address is one page lower than the memory area that is >>>>>> actually created in the process's virtual address space. Touc= hing an >>>>>> address in the "guard" page below the mapping will cause the m= apping >>>>>> to grow by a page. This growth can be repeated until the mappi= ng >>>>>> grows to within a page of the high end of the next lower mappi= ng, >>>>>> at which point touching the "guard" page will result in a SIGS= EGV >>>>>> signal. >>>>>> >>>>>> MAP_STACK (since Linux 2.6.27) >>>>>> Allocate the mapping at an address suitable for a process or t= hread >>>>>> stack. >>>>>> >>>>>> This flag is currently a no-op on Linux. However, by employing= this >>>>>> flag, applications can ensure that they transparently obtain s= upport >>>>>> if the flag is implemented in the future. Thus, it is used in = the >>>>>> glibc threading implementation to allow for the fact that >>>>>> some architectures may (later) require special treatment for >>>>>> stack allocations. A further reason to employ this flag is >>>>>> portability: MAP_STACK exists (and has an effect) on some >>>>>> other systems (e.g., some of the BSDs). >>>>>> >>>>>> The reason to suggest this change is, that on the parisc architectu= re the >>>>>> stack grows upwards. As such, using solely the MAP_GROWSDOWN flag w= ill not >>>>>> work. Note that there exists no MAP_GROWSUP flag. >>>>>> By changing the behaviour of MAP_STACK to mark the memory area with= the >>>>>> VM_STACK bit (which is VM_GROWSUP or VM_GROWSDOWN depending on the >>>>>> architecture) the MAP_STACK flag does exactly what people would exp= ect on >>>>>> all platforms. >>>>>> >>>>>> This change should have no negative side-effect, as all code which >>>>>> used mmap(MAP_GROWSDOWN | MAP_STACK) still work as before. >>>>>> >>>>>> Signed-off-by: Helge Deller >>>>>> >>>>>> diff --git a/include/linux/mman.h b/include/linux/mman.h >>>>>> index bcb201ab7a41..66bc72a0cb19 100644 >>>>>> --- a/include/linux/mman.h >>>>>> +++ b/include/linux/mman.h >>>>>> @@ -156,6 +156,7 @@ calc_vm_flag_bits(unsigned long flags) >>>>>> return _calc_vm_trans(flags, MAP_GROWSDOWN, VM_GROWSDOWN )= | >>>>>> _calc_vm_trans(flags, MAP_LOCKED, VM_LOCKED )= | >>>>>> _calc_vm_trans(flags, MAP_SYNC, VM_SYNC )= | >>>>>> + _calc_vm_trans(flags, MAP_STACK, VM_STACK ) | >>>>> >>>>> Right now MAP_STACK can be used to set VM_NOHUGEPAGE, but this will >>>>> change the user interface to create a vma that will grow. I'm not >>>>> entirely sure this is okay? >>>> >>>> AFAICT, I don't see this is a problem. Currently huge page also skips >>>> the VMAs with VM_GROWS* flags set. See vma_is_temporary_stack(). >>>> __thp_vma_allowable_orders() returns 0 if the vma is a temporary >>>> stack. >>> >>> If someone is using MAP_STACK to avoid having a huge page, they will >>> also get a mapping that grows - which is different than what happens >>> today. >>> >>> I'm not saying that's right, but someone could be abusing the existing >>> flag and this will change the behaviour. >> >> Wouldn't a plain mmap() followed by madvise(MADV_NOHUGEPAGE) do exactly= that? >> Why abusing MAP_STACK for that? > > Different sources and reports showed having huge pages for stack > mapping hurts performance. A lot of applications, for example, pthread > lib, allocate stack with MAP_STACK and they don't call MADV_NOHUGEPAGE > on stack mapping. That's true, and my patch does not change the behaviour wrt huge pages. Using MAP_STACK still tags the area VM_NOHUGEPAGE. See below... >>>>> That is mmap(MAP_STACK) would set VM_NOHUGEPAGE right now, with this >>>>> change you'd get VM_NOHUGEPAGE | VM_GROWS >>>>> >>>>>> _calc_vm_trans(flags, MAP_STACK, VM_NOHUGEPAGE)= | >>>>>> arch_calc_vm_flag_bits(flags); >>>>>> } >>