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Tue, 14 Dec 2021 06:33:02 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id OipvAZ46uGGpYwAAMHmgww (envelope-from ); Tue, 14 Dec 2021 06:33:02 +0000 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: b0174287-5ca7-11ec-85d3-df6b77346a89 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1639463582; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=zkOKhXkH4pkDY9AKrTFHL8kH6KTPVZJSV4sapU/Y16A=; b=KlSc8YUqYzyKyYZtLwIgDuXbf47EAznQqzkkfz90YWThEY/zAWJRbCurDVQgU2ZvfYUgpf a+FkdJUtlVlTybP/zap5EkXzZBDqBXUxyNIoWL/nvLMcf+2nhcInWCG0SoZTJcnvJ5u7FZ oawzglbUi39z+1xcHXJgDulb/LV1VAY= Subject: Re: [PATCH 02/10] mini-os: sort and sanitize e820 memory map To: Samuel Thibault , minios-devel@lists.xenproject.org, xen-devel@lists.xenproject.org, wl@xen.org References: <20211206072337.9517-1-jgross@suse.com> <20211206072337.9517-3-jgross@suse.com> <20211212000558.232nzs7k5lklpbym@begin> <20211213211907.lbjjnvayklf7qucb@begin> From: Juergen Gross Message-ID: <45aa9ea7-115e-af76-caf7-80b7d6f31163@suse.com> Date: Tue, 14 Dec 2021 07:33:01 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <20211213211907.lbjjnvayklf7qucb@begin> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="CbYhcGkjwpmxHpKbfaKiDsJjUJm4KHYTy" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --CbYhcGkjwpmxHpKbfaKiDsJjUJm4KHYTy Content-Type: multipart/mixed; boundary="lmMcK3byhWMpLkA5SAnQyF3zTT6EV3wTE"; protected-headers="v1" From: Juergen Gross To: Samuel Thibault , minios-devel@lists.xenproject.org, xen-devel@lists.xenproject.org, wl@xen.org Message-ID: <45aa9ea7-115e-af76-caf7-80b7d6f31163@suse.com> Subject: Re: [PATCH 02/10] mini-os: sort and sanitize e820 memory map References: <20211206072337.9517-1-jgross@suse.com> <20211206072337.9517-3-jgross@suse.com> <20211212000558.232nzs7k5lklpbym@begin> <20211213211907.lbjjnvayklf7qucb@begin> In-Reply-To: <20211213211907.lbjjnvayklf7qucb@begin> --lmMcK3byhWMpLkA5SAnQyF3zTT6EV3wTE Content-Type: multipart/mixed; boundary="------------576DF9A64280D1107F628895" Content-Language: en-US This is a multi-part message in MIME format. --------------576DF9A64280D1107F628895 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 13.12.21 22:19, Samuel Thibault wrote: > Juergen Gross, le lun. 13 d=C3=A9c. 2021 15:56:21 +0100, a ecrit: >> On 12.12.21 01:05, Samuel Thibault wrote: >>> Hello, >>> >>> Juergen Gross, le lun. 06 d=C3=A9c. 2021 08:23:29 +0100, a ecrit: >>>> - align the entries to page boundaries >>> >>>> + /* Adjust map entries to page boundaries. */ >>>> + for ( i =3D 0; i < e820_entries; i++ ) >>>> + { >>>> + end =3D (e820_map[i].addr + e820_map[i].size + PAGE_SIZE - = 1) & PAGE_MASK; >>>> + e820_map[i].addr &=3D PAGE_MASK; >>>> + e820_map[i].size =3D end - e820_map[i].addr; >>>> + } >>> >>> Mmm, what if the previous entry ends after the aligned start? >>> >>> On real machines that does happen, and you'd rather round up the star= t >>> address of usable areas, rather than rounding it down (and conversely= >>> for the end). >> >> I think you are partially right. :-) >> >> Entries for resources managed by Mini-OS (RAM, maybe NVME?) should be >> rounded to cover only complete pages (start rounded up, end rounded >> down), but all other entries should be rounded to cover the complete >> area (start rounded down, end rounded up) in order not to use any >> partial used page for e.g. mapping foreign pages. >=20 > Right! >=20 >>>> + /* Sort entries by start address. */ >>>> + for ( i =3D 0; i < e820_entries - 1; i++ ) >>>> + { >>>> + if ( e820_map[i].addr > e820_map[i + 1].addr ) >>>> + { >>>> + e820_swap_entries(i, i + 1); >>>> + i =3D -1; >>>> + } >>>> + } >>> >>> This looks O(n^3) to me? A bubble sort like this should be fine: >>> >>> /* Sort entries by start address. */ >>> for ( last =3D e820_entries; last > 1; last-- ) >>> { >>> for ( i =3D 0; i < last - 1; i++ ) >>> { >>> if ( e820_map[i].addr > e820_map[i + 1].addr ) >>> { >>> e820_swap_entries(i, i + 1); >>> } >>> } >>> } >> >> Hmm, depends. >> >> Assuming a rather well sorted map my version is O(n), while yours >> is still O(n^2). >=20 > Right, I was a bit lazy :) >=20 > This should be fine: >=20 > /* Sort entries by start address. */ > for ( i =3D 1; i < e820_entries; i++ ) > for ( j =3D i; j > 0 && e820_map[j-1].addr > e820_map[j].addr ) ; = j-- ) > e820_swap_entries(j - 1, j); >=20 >> I'm fine both ways, whatever you prefer. >=20 > I really prefer for loops which don't unexpectedly modify their loop > index, that's much less scary :) Agreed, I'll take your version. 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