Forwarding on behalf of Nishanth Menon: -----Original Message----- From: Menon, Nishanth Sent: Tuesday, March 17, 2009 8:17 AM To: 'linux-arm-kernel@xxxxxxxxxxxxxxxxxxxxxx' Cc: Gupta, Ramesh; Kevin Hilman; linux-omap@xxxxxxxxxxxxxxx; Ramirez Luna, Omar; Kanigeri, Hari; Ameya Palande; Guzman Lugo, Fernando; Ameya Palande Subject: dma_alloc_coherent fragmentation Looping in linux-arm ML: Discussion Ref: [1](linux-omap mailing list) While working with Linux OMAP kernel[2] we found that on allocating 4 meg chunks using dma_alloc_coherent and de-allocating with dma_free_coherent in a loop using a test driver[7], the memory is getting fragmented as shown by Ameya's observation [3] finally resulting in dump_stack due to lack of pages. Searching through previous archives, found [4] which seem to imply that allocating chunks greater than 1 page could cause fragmentation. I wonder why we see this even if we allocate and free the memory in sequence as in [5]. This seems to happen on 2.6.28 and 2.6.29 but not on the 2.6.27 based kernel[6]. Regards, Nishanth Menon Ref: [1] http://marc.info/?t=123719779100002&r=1&w=2 [2] http://git.kernel.org/?p=linux/kernel/git/tmlind/linux-omap-2.6.git [3] http://marc.info/?l=linux-omap&m=123722460022336&w=2 [4] http://lkml.indiana.edu/hypermail/linux/kernel/0706.0/0370.html [5] http://marc.info/?l=linux-omap&m=123719772811746&w=2 [6] http://git.omapzoom.com/?p=repo/omapkernel.git; [7] http://marc.info/?l=linux-omap&m=123719772811746&q=p3 ��.n��������+%������w��{.n�����{�������ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f
