From: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> To: Andi Kleen <andi@firstfloor.org> Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andi Kleen <ak@linux.intel.com>, Hillf Danton <dhillf@gmail.com> Subject: Re: [PATCH] MM: Support more pagesizes for MAP_HUGETLB/SHM_HUGETLB v6 Date: Mon, 22 Oct 2012 15:56:13 +0200 [thread overview] Message-ID: <CAKgNAkgQ6JZdwOsCAQ4Ak_gVXtav=TzgzW2tbk5jMUwxtMqOAg@mail.gmail.com> (raw) In-Reply-To: <20121022133534.GR16230@one.firstfloor.org> On Mon, Oct 22, 2012 at 3:35 PM, Andi Kleen <andi@firstfloor.org> wrote: > On Mon, Oct 22, 2012 at 03:27:33PM +0200, Andi Kleen wrote: >> > Maybe I am missing something obvious, but does this not conflict with >> > include/uapi/asm-generic/mman-common.h: >> > >> > #ifdef CONFIG_MMAP_ALLOW_UNINITIALIZED >> > # define MAP_UNINITIALIZED 0x4000000 >> > ... >> > >> > 0x4000000 == (1 << 26 >> > >> >> You're right. Someone added that since I wrote the patch originally. >> I owned them when originally submitted @) Thanks for catching. >> >> Have to move my bits two up, which will still work, but limit the > > Two up won't work, need one up. > > 32..28 = 16 is too small for 2^30 = 1GB pages > 32..27 = 32 max 4GB pages Not sure of your notation there. I assume 31..27 means 5 bits (32 through to 28 inclusive, 27 excluded). That gives you just 2^31 == 2GB, not 4GB (unless your planning to always add 1 to the value in those bits, since a value of zero has little meaning). But there seems an obvious solution here: given your value in those bits (call it 'n'), the why not apply a multiplier. I mean, certainly you never want a value <= 12 for n, and I suspect that the reasonable minimum could be much larger (e.g., 2^16). Call that minimum M. Then you could interpret the value in your bits as meaning a page size of (2^n) * M > So this will use up all remaining flag bits now. On the other hand, that seems really bad. It looks like that kills the ability to further extend the mmap() API with new flags in the future. It doesn't sound like we should be doing that. Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Author of "The Linux Programming Interface"; http://man7.org/tlpi/
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From: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> To: Andi Kleen <andi@firstfloor.org> Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andi Kleen <ak@linux.intel.com>, Hillf Danton <dhillf@gmail.com> Subject: Re: [PATCH] MM: Support more pagesizes for MAP_HUGETLB/SHM_HUGETLB v6 Date: Mon, 22 Oct 2012 15:56:13 +0200 [thread overview] Message-ID: <CAKgNAkgQ6JZdwOsCAQ4Ak_gVXtav=TzgzW2tbk5jMUwxtMqOAg@mail.gmail.com> (raw) In-Reply-To: <20121022133534.GR16230@one.firstfloor.org> On Mon, Oct 22, 2012 at 3:35 PM, Andi Kleen <andi@firstfloor.org> wrote: > On Mon, Oct 22, 2012 at 03:27:33PM +0200, Andi Kleen wrote: >> > Maybe I am missing something obvious, but does this not conflict with >> > include/uapi/asm-generic/mman-common.h: >> > >> > #ifdef CONFIG_MMAP_ALLOW_UNINITIALIZED >> > # define MAP_UNINITIALIZED 0x4000000 >> > ... >> > >> > 0x4000000 == (1 << 26 >> > >> >> You're right. Someone added that since I wrote the patch originally. >> I owned them when originally submitted @) Thanks for catching. >> >> Have to move my bits two up, which will still work, but limit the > > Two up won't work, need one up. > > 32..28 = 16 is too small for 2^30 = 1GB pages > 32..27 = 32 max 4GB pages Not sure of your notation there. I assume 31..27 means 5 bits (32 through to 28 inclusive, 27 excluded). That gives you just 2^31 == 2GB, not 4GB (unless your planning to always add 1 to the value in those bits, since a value of zero has little meaning). But there seems an obvious solution here: given your value in those bits (call it 'n'), the why not apply a multiplier. I mean, certainly you never want a value <= 12 for n, and I suspect that the reasonable minimum could be much larger (e.g., 2^16). Call that minimum M. Then you could interpret the value in your bits as meaning a page size of (2^n) * M > So this will use up all remaining flag bits now. On the other hand, that seems really bad. It looks like that kills the ability to further extend the mmap() API with new flags in the future. It doesn't sound like we should be doing that. Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Author of "The Linux Programming Interface"; http://man7.org/tlpi/ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2012-10-22 13:56 UTC|newest] Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top 2012-10-19 16:48 [PATCH] MM: Support more pagesizes for MAP_HUGETLB/SHM_HUGETLB v6 Andi Kleen 2012-10-19 16:48 ` Andi Kleen 2012-10-20 3:39 ` Hillf Danton 2012-10-20 3:39 ` Hillf Danton 2012-10-22 11:27 ` Michael Kerrisk 2012-10-22 11:27 ` Michael Kerrisk 2012-10-22 13:27 ` Andi Kleen 2012-10-22 13:27 ` Andi Kleen 2012-10-22 13:35 ` Andi Kleen 2012-10-22 13:35 ` Andi Kleen 2012-10-22 13:56 ` Michael Kerrisk (man-pages) [this message] 2012-10-22 13:56 ` Michael Kerrisk (man-pages) 2012-10-22 15:36 ` Andi Kleen 2012-10-22 15:36 ` Andi Kleen 2012-10-22 15:53 ` Michael Kerrisk (man-pages) 2012-10-22 15:53 ` Michael Kerrisk (man-pages) 2012-10-22 16:11 ` Andi Kleen 2012-10-22 16:11 ` Andi Kleen 2012-10-22 16:23 ` Michael Kerrisk (man-pages) 2012-10-22 16:23 ` Michael Kerrisk (man-pages) 2012-10-22 16:29 ` Andi Kleen 2012-10-22 16:29 ` Andi Kleen 2012-10-22 16:42 ` Michael Kerrisk (man-pages) 2012-10-22 16:42 ` Michael Kerrisk (man-pages) 2012-10-23 1:45 ` Benjamin Herrenschmidt 2012-10-23 1:45 ` Benjamin Herrenschmidt 2012-10-23 1:44 ` Benjamin Herrenschmidt 2012-10-23 1:44 ` Benjamin Herrenschmidt 2012-10-23 2:28 ` Andi Kleen 2012-10-23 2:28 ` Andi Kleen 2012-10-23 7:37 ` Michael Kerrisk (man-pages) 2012-10-23 7:37 ` Michael Kerrisk (man-pages) 2012-10-23 13:39 ` Andi Kleen 2012-10-23 13:39 ` Andi Kleen 2012-10-23 22:56 ` Valdis.Kletnieks 2012-10-22 21:39 ` Andrew Morton 2012-10-22 21:39 ` Andrew Morton
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