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Shutemov" , mark.rutland@arm.com, Mel Gorman , Minchan Kim , Ingo Molnar , namhyung@kernel.org, "Peter Zijlstra (Intel)" , Randy Dunlap , Rik van Riel , David Rientjes , Steven Rostedt , rppt@kernel.org, sblbir@amazon.com, shuah@kernel.org, sj38.park@gmail.com, snu@amazon.de, Vlastimil Babka , Vladimir Davydov , Yang Shi , Huang Ying , linux-damon@amazon.com, Linux MM , linux-doc@vger.kernel.org, LKML Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: DEE7F18038B64 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Jul 17, 2020 at 9:24 AM SeongJae Park wrote: > > On Fri, 17 Jul 2020 08:17:09 -0700 Shakeel Butt wrote: > > > On Thu, Jul 16, 2020 at 11:54 PM SeongJae Park wrote: > > > > > > On Thu, 16 Jul 2020 17:46:54 -0700 Shakeel Butt wrote: > > > > > > > On Mon, Jul 13, 2020 at 1:44 AM SeongJae Park wrote: > > > > > > > > > > From: SeongJae Park > > > > > > > > > > This commit introduces a reference implementation of the address space > > > > > specific low level primitives for the virtual address space, so that > > > > > users of DAMON can easily monitor the data accesses on virtual address > > > > > spaces of specific processes by simply configuring the implementation to > > > > > be used by DAMON. > > > > > > > > > > The low level primitives for the fundamental access monitoring are > > > > > defined in two parts: > > > > > 1. Identification of the monitoring target address range for the address > > > > > space. > > > > > 2. Access check of specific address range in the target space. > > > > > > > > > > The reference implementation for the virtual address space provided by > > > > > this commit is designed as below. > > > > > > > > > > PTE Accessed-bit Based Access Check > > > > > ----------------------------------- > > > > > > > > > > The implementation uses PTE Accessed-bit for basic access checks. That > > > > > is, it clears the bit for next sampling target page and checks whether > > > > > it set again after one sampling period. To avoid disturbing other > > > > > Accessed bit users such as the reclamation logic, the implementation > > > > > adjusts the ``PG_Idle`` and ``PG_Young`` appropriately, as same to the > > > > > 'Idle Page Tracking'. > > > > > > > > > > VMA-based Target Address Range Construction > > > > > ------------------------------------------- > > > > > > > > > > Only small parts in the super-huge virtual address space of the > > > > > processes are mapped to physical memory and accessed. Thus, tracking > > > > > the unmapped address regions is just wasteful. However, because DAMON > > > > > can deal with some level of noise using the adaptive regions adjustment > > > > > mechanism, tracking every mapping is not strictly required but could > > > > > even incur a high overhead in some cases. That said, too huge unmapped > > > > > areas inside the monitoring target should be removed to not take the > > > > > time for the adaptive mechanism. > > > > > > > > > > For the reason, this implementation converts the complex mappings to > > > > > three distinct regions that cover every mapped area of the address > > > > > space. Also, the two gaps between the three regions are the two biggest > > > > > unmapped areas in the given address space. The two biggest unmapped > > > > > areas would be the gap between the heap and the uppermost mmap()-ed > > > > > region, and the gap between the lowermost mmap()-ed region and the stack > > > > > in most of the cases. Because these gaps are exceptionally huge in > > > > > usual address spacees, excluding these will be sufficient to make a > > > > > reasonable trade-off. Below shows this in detail:: > > > > > > > > > > > > > > > > > > > > > > > > > (small mmap()-ed regions and munmap()-ed regions) > > > > > > > > > > > > > > > > > > > > > > > > > Signed-off-by: SeongJae Park > > > > > Reviewed-by: Leonard Foerster > > > > [snip] > > > > > + > > > > > +static void damon_mkold(struct mm_struct *mm, unsigned long addr) > > > > > +{ > > > > > + pte_t *pte = NULL; > > > > > + pmd_t *pmd = NULL; > > > > > + spinlock_t *ptl; > > > > > + > > > > > + if (follow_pte_pmd(mm, addr, NULL, &pte, &pmd, &ptl)) > > > > > + return; > > > > > + > > > > > + if (pte) { > > > > > + if (pte_young(*pte)) { > > > > > > > > Any reason for skipping mmu_notifier_clear_young()? Why exclude VMs as > > > > DAMON's target applications? > > > > > > Obviously my mistake, thank you for pointing this! I will add the function > > > call in the next spin. > > > > > > > Similarly mmu_notifier_test_young() for the damon_young(). > > Yes, indeed. Thanks for pointing this, either :) > > > BTW I think we can combine ctx->prepare_access_checks() and > > ctx->check_accesses() into one i.e. get the young state for the previous > > cycle and mkold for the next cycle in a single step. > > Yes, we could. But, I'm unsure what is the advantage of doing that. First of > all, if the combined implementation is required, peopld could simply implement > the two logics in the combined way in one of the callbacks and leave the other > one blank. Also, I'm worrying if combining those could make the code a little > bit hard to read. IMHO, I think separating those makes the 'kdamond_fn()' code > little bit easier to read. Actually, I started from the combined approach but > separated the two logics since v7 after Jonathan's comment[1]. > > > [1] https://lore.kernel.org/linux-mm/20200310085721.00000a0f@Huawei.com/ > > > > > > I am wondering if there is any advantage to having "Page Idle > > Tracking" beside DAMON. I think we can make them mutually exclusive. > > Once we have established that I think DAMON can steal the two page > > flag bits from it and can make use of them. What do you think? > > Again, yes, I think we could. But I don't see clear advantage of it for now. > > Hmm, I will think more about it. Somehow I feel if we want to monitor at the page sized region granularity then this will be really helpful. Anyways, it needs more brainstorming. BTW I am still going over the series and my humble request would be to wait till I have gone through the series completely and provided the feedback then you can send the next version after incorporating the feedback. Shakeel