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Date: Thu, 24 Jul 2014 13:53:58 +0800 From: "Zhang, Yanmin" <yanmin_zhang@...ux.intel.com> To: Mikulas Patocka <mpatocka@...hat.com>, Alasdair G Kergon <agk@...hat.com> CC: "xinhui.pan" <xinhuix.pan@...el.com>, linux-kernel@...r.kernel.org, snitzer@...hat.com, dm-devel@...hat.com, "Liu, ShuoX" <shuox.liu@...el.com> Subject: Re: [dm-devel] [PATCH] md/dm-ioctl.c: optimize memory allocation in copy_params On 2014/7/24 1:14, Mikulas Patocka wrote: > > On Wed, 23 Jul 2014, Alasdair G Kergon wrote: > >> On Wed, Jul 23, 2014 at 08:16:58AM -0400, Mikulas Patocka wrote: >>> So, it means that you do not use device mapper at all. So, why are you >>> trying to change memory allocation in device mapper? >> >> So the *test* they run is asking device-mapper to briefly reserve a 64KB >> buffer when there is no data to report: The answer is not to run that >> pointless test:) >> >> And if a single 64KB allocation really is a big deal, then patch 'vold' >> in userspace so it doesn't ask for 64KB when it clearly doesn't need it! >> >> + int Devmapper::dumpState(SocketClient *c) { >> + char *buffer = (char *) malloc(1024 * 64); >> >> The code has just >> #define DEVMAPPER_BUFFER_SIZE 4096 >> for all the other dm ioctls it issues. >> >> Only use a larger value when it is needed i.e. if DM_BUFFER_FULL_FLAG gets set. >> >> Alasdair > Device mapper shouldn't depend on allocation on any contiguous memory - it > will fall back to vmalloc. I still can't believe that their suggested > patch makes any difference. > > This pattern is being repeated over and over in the kernel - for example: > > if (PIDLIST_TOO_LARGE(count)) > return vmalloc(count * sizeof(pid_t)); > else > return kmalloc(count * sizeof(pid_t), GFP_KERNEL); > > > if (is_vmalloc_addr(p)) > vfree(p); > else > kfree(p); > > - I think we should make two functions that do this operation (for example > kvalloc and kvfree) and convert device mapper and other users to these > functions. Then, other kernel subsystems can start to use them to fix > memory fragmentation issues. Thank Mikulas and Alasdair. Before sending out the patch, we know the result. :) It's hard to balance between performance and stability. Anyway, we would try to change seq_read. Yanmin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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