From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 6 Aug 1999 23:11:58 -0400 Message-Id: <199908070311.XAA03580@skydive.ai.mit.edu> Subject: mmap doesn't "wrap?" From: grg22@ai.mit.edu Sender: owner-linux-mm@kvack.org Return-Path: To: Linux-MM@kvack.org, grg22@ai.mit.edu List-ID: It looks to me as though mmap will try to grab a region of memory whose address is greater than or equal to the suggested start address passed in the call. I suppose it does this because it traverses the free list in ascending address order. If it can't find enough memory above the requested address, then the mmap fails, claiming ENOMEM; and it does this even when you've got gigs of wide open address space below the suggested address. One effect of this is that if you specify an address of 0 (saying "I don't care"), the mmap seems to start above 0x40000000 by default, and forever ignores the gigabyte of address space below that. This seems undesirable, especially when your chunk of memory requested would fit below 0x4000000 but can't fit above it (due to memory fragmentation, or because you've already used up the rest of it!). I don't know if the right thing would be to change the behavior of get_unmapped_area() to "wrap" from the beginning of the free list when it can't find anything above the given address, or just add a failure clause into do_mmap() to try again starting from 0 (or something else?). (Yes, I've patched my rlimits so I can access 3GB virtual and yes, I commit the sin of addressing the 32-bit community only on this more general mailing list: apologies to you lucky 64-bit folks.) thx, grg -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://humbolt.geo.uu.nl/Linux-MM/