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Date: Mon, 19 Mar 2012 17:18:35 -0700 From: John Stultz <john.stultz@...aro.org> To: Dmitry Adamushko <dmitry.adamushko@...il.com> CC: linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>, Android Kernel Team <kernel-team@...roid.com>, Robert Love <rlove@...gle.com>, Mel Gorman <mel@....ul.ie>, Hugh Dickins <hughd@...gle.com>, Dave Hansen <dave@...ux.vnet.ibm.com>, Rik van Riel <riel@...hat.com>, Dave Chinner <david@...morbit.com>, Neil Brown <neilb@...e.de>, Andrea Righi <andrea@...terlinux.com>, "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> Subject: Re: [PATCH 2/2] [RFC] fadvise: Add _VOLATILE,_ISVOLATILE, and _NONVOLATILE flags On 03/17/2012 09:21 AM, Dmitry Adamushko wrote: > Hi John, > > [ ... ] > >> +/* >> + * Mark a region as volatile, allowing dirty pages to be purged >> + * under memory pressure >> + */ >> +long mapping_range_volatile(struct address_space *mapping, >> + pgoff_t start_index, pgoff_t end_index) >> +{ >> + struct volatile_range *new; >> + struct range_tree_node *node; >> + >> + u64 start, end; >> + int purged = 0; >> + start = (u64)start_index; >> + end = (u64)end_index; >> + >> + new = vrange_alloc(); >> + if (!new) >> + return -ENOMEM; >> + >> + mutex_lock(&volatile_mutex); >> + >> + node = range_tree_in_range_adjacent(&mapping->volatile_root, >> + start, end); >> + while (node) { >> + struct volatile_range *vrange; >> + >> + /* Already entirely marked volatile, so we're done */ >> + if (node->start< start&& node->end> end) { >> + /* don't need the allocated value */ >> + kfree(new); >> + goto out; >> + } >> + >> + /* Grab containing volatile range */ >> + vrange = container_of(node, struct volatile_range, range_node); >> + >> + /* resize range */ >> + start = min_t(u64, start, node->start); >> + end = max_t(u64, end, node->end); >> + purged |= vrange->purged; >> + >> + >> + vrange_del(vrange); >> + >> + /* get the next possible overlap */ >> + node = range_tree_in_range(&mapping->volatile_root, start, end); > I guess range_tree_in_range_adjacent() should be used here again. > There can be 2 adjacent regions (left and right), and we'll miss one > of them with range_tree_in_range(). Good catch, thank you! > Also (as I had already mentioned before), I think that new ranges must > not be merged with the existing "vrange->purged == 1" ranges. > Otherwise, for some use cases, the whole idea of 'volatility' gets > broken. For example, when an application is processing a big buffer in > small consequent chunks (marking a chunk as volatile when done with > it), and the range gets 'purged' by the kernel early in this process > (when it's still small). > I agree that this seems like a much more intelligent way coalesce regions. I hadn't yet implemented it, as I was hoping for some comment from the Android folks if there was a specific use for the design they selected for ashmem, but I suspect there isn't. I'll go ahead and integrate this for the next revision. Thanks again for the feedback! -john -- 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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