----- Original Message ----- > From: Colin Cross <ccross@xxxxxxxxxxx> > To: pintu.k@xxxxxxxxxxx > Cc: Laura Abbott <lauraa@xxxxxxxxxxxxxx>; Heesub Shin <heesub.shin@xxxxxxxxxxx>; "akpm@xxxxxxxxxxxxxxxxxxxx" <akpm@xxxxxxxxxxxxxxxxxxxx>; "gregkh@xxxxxxxxxxxxxxxxxxx" <gregkh@xxxxxxxxxxxxxxxxxxx>; "john.stultz@xxxxxxxxxx" <john.stultz@xxxxxxxxxx>; "rebecca@xxxxxxxxxxx" <rebecca@xxxxxxxxxxx>; "devel@xxxxxxxxxxxxxxxxxxxx" <devel@xxxxxxxxxxxxxxxxxxxx>; "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>; IQBAL SHAREEF <iqbal.ams@xxxxxxxxxxx>; "pintu_agarwal@xxxxxxxxx" <pintu_agarwal@xxxxxxxxx>; Vishnu Pratap Singh <vishnu.ps@xxxxxxxxxxx>; "cpgs@xxxxxxxxxxx" <cpgs@xxxxxxxxxxx> > Sent: Monday, 6 October 2014 11:01 PM > Subject: Re: Re: [PATCH 1/1] [ion]: system-heap use PAGE_ALLOC_COSTLY_ORDER for high order > > On Mon, Oct 6, 2014 at 9:26 AM, PINTU KUMAR <pintu.k@xxxxxxxxxxx> wrote: > >> >> Hi, >> >________________________________ >> > From: Laura Abbott <lauraa@xxxxxxxxxxxxxx> >> >To: Heesub Shin <heesub.shin@xxxxxxxxxxx>; Pintu Kumar > <pintu.k@xxxxxxxxxxx>; akpm@xxxxxxxxxxxxxxxxxxxx; > gregkh@xxxxxxxxxxxxxxxxxxx; john.stultz@xxxxxxxxxx; rebecca@xxxxxxxxxxx; > ccross@xxxxxxxxxxx; devel@xxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx >> >Cc: iqbal.ams@xxxxxxxxxxx; pintu_agarwal@xxxxxxxxx; > vishnu.ps@xxxxxxxxxxx >> >Sent: Monday, 6 October 2014 7:37 PM >> >Subject: Re: [PATCH 1/1] [ion]: system-heap use PAGE_ALLOC_COSTLY_ORDER > for high order >> > >> > >> >On 10/6/2014 3:27 AM, Heesub Shin wrote: >> > >> > >> > >> > >> >> Hello Kumar, >> >> >> >> On 10/06/2014 05:31 PM, Pintu Kumar wrote: >> >>> The Android ion_system_heap uses allocation fallback mechanism >> >>> based on 8,4,0 order pages available in the system. >> >>> It changes gfp flags based on higher order allocation request. >> >>> This higher order value is hard-coded as 4, instead of using >> >>> the system defined higher order value. >> >>> Thus replacing this hard-coded value with > PAGE_ALLOC_COSTLY_ORDER >> >>> which is defined as 3. >> >>> This will help mapping the higher order request in system heap > with >> >>> the actual allocation request. >> >> >> >> Quite reasonable. >> >> >> >> Reviewed-by: Heesub Shin <heesub.shin@xxxxxxxxxxx> >> >> >> >> BTW, Anyone knows how the allocation order (8,4 and 0) was > decided? I >> >> think only Google guys might know the answer. >> >> >> >> regards, >> >> heesub >> >> >> > >> >My understanding was this was completely unrelated to the costly order >> >and was related to the page sizes corresponding to IOMMU page sizes >> >(1MB, 64K, 4K). This won't make a difference for the uncached page >> >pool case but for the not page pool case, I'm not sure if there > would >> >be a benefit for trying to get 32K pages with some effort vs. just >> >going back to 4K pages. >> >> No, it is not just related to IOMMU case. It comes into picture also for >> normal system-heap allocation (without iommu cases). >> Also, it is applicable for both uncached and page_pool cases. >> Please also check the changes under ion_system_heap_create. >> Here the gfp_flags are set under the pool structure. >> This value is used in ion_page_pool_alloc_pages. >> In both the cases, it internally calls alloc_pages, with this gfp_flags. >> Now, during memory pressure scenario, when alloc_pages moves to slowpath >> this gfp_flags will be used to decide allocation retry. >> In the current code, the higher-order flag is set only when order is > greater than 4. >> But, in MM, the order 4 is also considered as higher-order request. >> This higher-order is decided based on PAGE_ALLOC_COSTLY_ORDER (3) value. >> Hence, I think this value should be in sync with the MM code. >> > >> >Do you have any data/metrics that show a benefit from this patch? >> I think it is not related to any data or metrics. >> It is about replacing the hard-coded higher-order check to be in sync with >> the MM code. >> > > The selection of the orders used for allocation (8, then 4, then 0) is > designed to match with the sizes often found in IOMMUs, but this isn't > changing the order of the allocation, it is changing the GFP flags > used for the order 4 allocation. Right now we are using the > low_order_gfp_flags for order 4, this patch would change it to use > high_order_gfp_flags. We originally used low_order_gfp_flags here > because the MM subsystem can usually satisfy these allocations, and > the additional load placed on the MM subsystem to kick off kswapd to > free up more order 4 chunks is generally worth it. Using order 4 > pages instead of order 0 pages can significantly improve the > performance of many IOMMUs by reducing TLB pressure and time spent > updating page tables. Unless you have data showing that this improves > something, and doesn't just cause all allocations to be order 0 when > under memory pressure, I don't suggest merging this. > Ok agree. It is worth retrying the allocation with order-4 pages. But, since 4 is considered higher order for MM and is greater than PAGE_ALLOC_COSTLY_ORDER. I guess the retrying will not happen, because of the following check in page_alloc: if (order > PAGE_ALLOC_COSTLY_ORDER) goto nopage; _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
