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<07270e29-c9d4-ae8c-a236-eb6fefccbf6c@arm.com> Content-Language: en-GB Cc: vinmenon@codeaurora.org, kernel-team@android.com X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" CgpPbiA5LzE4LzIwMjAgNzo0OCBQTSwgUm9iaW4gTXVycGh5IHdyb3RlOgo+IE9uIDIwMjAtMDgt MjAgMTM6NDksIHZqaXR0YUBjb2RlYXVyb3JhLm9yZyB3cm90ZToKPj4gRnJvbTogVmlqYXlhbmFu ZCBKaXR0YSA8dmppdHRhQGNvZGVhdXJvcmEub3JnPgo+Pgo+PiBXaGVuIGV2ZXIgYSBuZXcgaW92 YSBhbGxvYyByZXF1ZXN0IGNvbWVzIGlvdmEgaXMgYWx3YXlzIHNlYXJjaGVkCj4+IGZyb20gdGhl IGNhY2hlZCBub2RlIGFuZCB0aGUgbm9kZXMgd2hpY2ggYXJlIHByZXZpb3VzIHRvIGNhY2hlZAo+ PiBub2RlLiBTbywgZXZlbiBpZiB0aGVyZSBpcyBmcmVlIGlvdmEgc3BhY2UgYXZhaWxhYmxlIGlu 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smtp.codeaurora.org 47B5CC433CB Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; spf=fail smtp.mailfrom=vjitta@codeaurora.org Subject: Re: [PATCH v2 1/2] iommu/iova: Retry from last rb tree node if iova search fails To: Robin Murphy , joro@8bytes.org, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org Cc: vinmenon@codeaurora.org, kernel-team@android.com References: <1597927761-24441-1-git-send-email-vjitta@codeaurora.org> <07270e29-c9d4-ae8c-a236-eb6fefccbf6c@arm.com> From: Vijayanand Jitta Message-ID: <8efbdd09-8f0f-e6fe-ab82-db08f6d5b5b5@codeaurora.org> Date: Wed, 30 Sep 2020 11:18:12 +0530 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <07270e29-c9d4-ae8c-a236-eb6fefccbf6c@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/18/2020 7:48 PM, Robin Murphy wrote: > On 2020-08-20 13:49, vjitta@codeaurora.org wrote: >> From: Vijayanand Jitta >> >> When ever a new iova alloc request comes iova is always searched >> from the cached node and the nodes which are previous to cached >> node. So, even if there is free iova space available in the nodes >> which are next to the cached node iova allocation can still fail >> because of this approach. >> >> Consider the following sequence of iova alloc and frees on >> 1GB of iova space >> >> 1) alloc - 500MB >> 2) alloc - 12MB >> 3) alloc - 499MB >> 4) free -  12MB which was allocated in step 2 >> 5) alloc - 13MB >> >> After the above sequence we will have 12MB of free iova space and >> cached node will be pointing to the iova pfn of last alloc of 13MB >> which will be the lowest iova pfn of that iova space. Now if we get an >> alloc request of 2MB we just search from cached node and then look >> for lower iova pfn's for free iova and as they aren't any, iova alloc >> fails though there is 12MB of free iova space. >> >> To avoid such iova search failures do a retry from the last rb tree node >> when iova search fails, this will search the entire tree and get an iova >> if its available. >> >> Signed-off-by: Vijayanand Jitta >> --- >>   drivers/iommu/iova.c | 23 +++++++++++++++++------ >>   1 file changed, 17 insertions(+), 6 deletions(-) >> >> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c >> index 49fc01f..4e77116 100644 >> --- a/drivers/iommu/iova.c >> +++ b/drivers/iommu/iova.c >> @@ -184,8 +184,9 @@ static int __alloc_and_insert_iova_range(struct >> iova_domain *iovad, >>       struct rb_node *curr, *prev; >>       struct iova *curr_iova; >>       unsigned long flags; >> -    unsigned long new_pfn; >> +    unsigned long new_pfn, low_pfn_new; >>       unsigned long align_mask = ~0UL; >> +    unsigned long high_pfn = limit_pfn, low_pfn = iovad->start_pfn; >>         if (size_aligned) >>           align_mask <<= fls_long(size - 1); >> @@ -198,15 +199,25 @@ static int __alloc_and_insert_iova_range(struct >> iova_domain *iovad, >>         curr = __get_cached_rbnode(iovad, limit_pfn); >>       curr_iova = rb_entry(curr, struct iova, node); >> +    low_pfn_new = curr_iova->pfn_hi + 1; > > Could we call "low_pfn_new" something like "retry_pfn" instead? This > code already has unavoidable readability struggles with so many > different "pfn"s in play, so having two different meanings of "new" > really doesn't help. > > Other than that, I think this looks OK (IIRC it's basically what I > originally suggested), so with the naming tweaked, > > Reviewed-by: Robin Murphy > Thanks for review, I have renamed it to retry_pfn in v4. Thanks, Vijay >> + >> +retry: >>       do { >> -        limit_pfn = min(limit_pfn, curr_iova->pfn_lo); >> -        new_pfn = (limit_pfn - size) & align_mask; >> +        high_pfn = min(high_pfn, curr_iova->pfn_lo); >> +        new_pfn = (high_pfn - size) & align_mask; >>           prev = curr; >>           curr = rb_prev(curr); >>           curr_iova = rb_entry(curr, struct iova, node); >> -    } while (curr && new_pfn <= curr_iova->pfn_hi); >> - >> -    if (limit_pfn < size || new_pfn < iovad->start_pfn) { >> +    } while (curr && new_pfn <= curr_iova->pfn_hi && new_pfn >= >> low_pfn); >> + >> +    if (high_pfn < size || new_pfn < low_pfn) { >> +        if (low_pfn == iovad->start_pfn && low_pfn_new < limit_pfn) { >> +            high_pfn = limit_pfn; >> +            low_pfn = low_pfn_new; >> +            curr = &iovad->anchor.node; >> +            curr_iova = rb_entry(curr, struct iova, node); >> +            goto retry; >> +        } >>           iovad->max32_alloc_size = size; >>           goto iova32_full; >>       } >> -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation