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Date: Wed, 11 Jul 2012 09:15:43 -0500 From: Seth Jennings <sjenning@...ux.vnet.ibm.com> To: Minchan Kim <minchan@...nel.org> CC: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Andrew Morton <akpm@...ux-foundation.org>, Dan Magenheimer <dan.magenheimer@...cle.com>, Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>, Nitin Gupta <ngupta@...are.org>, Robert Jennings <rcj@...ux.vnet.ibm.com>, linux-mm@...ck.org, devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 3/4] zsmalloc: add details to zs_map_object boiler plate On 07/11/2012 02:42 AM, Minchan Kim wrote: > On 07/11/2012 12:17 AM, Seth Jennings wrote: >> On 07/09/2012 09:35 PM, Minchan Kim wrote: >>> Maybe we need local_irq_save/restore in zs_[un]map_object path. >> >> I'd rather not disable interrupts since that will create >> unnecessary interrupt latency for all users, even if they > > Agreed. > Although we guide k[un]map atomic is so fast, it isn't necessary > to force irq_[enable|disable]. Okay. > >> don't need interrupt protection. If a particular user uses >> zs_map_object() in an interrupt path, it will be up to that >> user to disable interrupts to ensure safety. > > Nope. It shouldn't do that. > Any user in interrupt context can't assume that there isn't any other user using per-cpu buffer > right before interrupt happens. > > The concern is that if such bug happens, it's very hard to find a bug. > So, how about adding this? > > void zs_map_object(...) > { > BUG_ON(in_interrupt()); > } I not completely following you, but I think I'm following enough. Your point is that the per-cpu buffers are shared by all zsmalloc users and one user doesn't know if another user is doing a zs_map_object() in an interrupt path. However, I think what you are suggesting is to disallow mapping in interrupt context. This is a problem for zcache as it already does mapping in interrupt context, namely for page decompression in the page fault handler. What do you think about making the per-cpu buffers local to each zsmalloc pool? That way each user has their own per-cpu buffers and don't step on each other's toes. Thanks, Seth -- 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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