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[213.175.37.10]) by smtp.gmail.com with ESMTPSA id f1sm21994131wmc.45.2020.01.20.02.21.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 20 Jan 2020 02:21:39 -0800 (PST) From: Vitaly Kuznetsov To: Michael Kelley , "lantianyu1986\@gmail.com" , KY Srinivasan , Haiyang Zhang , Stephen Hemminger , "sashal\@kernel.org" Cc: Tianyu Lan , "linux-hyperv\@vger.kernel.org" , "linux-kernel\@vger.kernel.org" , "stable\@vger.kernel.org" Subject: RE: [PATCH V2] x86/Hyper-V: Balloon up according to request page number In-Reply-To: References: <20200116141600.23391-1-Tianyu.Lan@microsoft.com> Date: Mon, 20 Jan 2020 11:21:38 +0100 Message-ID: <87v9p6fmx9.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-hyperv-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-hyperv@vger.kernel.org Michael Kelley writes: > From: Tianyu Lan Sent: Thursday, January 16, 2020 6:16 AM >> >> Current code has assumption that balloon request memory size aligns >> with 2MB. But actually Hyper-V doesn't guarantee such alignment. When >> balloon driver receives non-aligned balloon request, it produces warning >> and balloon up more memory than requested in order to keep 2MB alignment. >> Remove the warning and balloon up memory according to actual requested >> memory size. >> >> Fixes: f6712238471a ("hv: hv_balloon: avoid memory leak on alloc_error of 2MB memory >> block") >> Cc: stable@vger.kernel.org >> Signed-off-by: Tianyu Lan >> --- >> Change since v2: >> - Change logic of switching alloc_unit from 2MB to 4KB >> in the balloon_up() to avoid redundant iteration when >> handle non-aligned page request. >> - Remove 2MB alignment operation and comment in balloon_up() >> --- >> drivers/hv/hv_balloon.c | 12 ++++-------- >> 1 file changed, 4 insertions(+), 8 deletions(-) >> >> diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c >> index 7f3e7ab22d5d..536807efbc35 100644 >> --- a/drivers/hv/hv_balloon.c >> +++ b/drivers/hv/hv_balloon.c >> @@ -1684,7 +1684,7 @@ static unsigned int alloc_balloon_pages(struct >> hv_dynmem_device *dm, >> if (num_pages < alloc_unit) >> return 0; > > The above test is no longer necessary. The num_pages < alloc_unit > case is handled implicitly by your new 'for' loop condition. > >> >> - for (i = 0; (i * alloc_unit) < num_pages; i++) { >> + for (i = 0; i < num_pages / alloc_unit; i++) { >> if (bl_resp->hdr.size + sizeof(union dm_mem_page_range) > >> HV_HYP_PAGE_SIZE) >> return i * alloc_unit; >> @@ -1722,7 +1722,7 @@ static unsigned int alloc_balloon_pages(struct >> hv_dynmem_device *dm, >> >> } >> >> - return num_pages; >> + return i * alloc_unit; >> } >> >> static void balloon_up(union dm_msg_info *msg_info) >> @@ -1737,9 +1737,6 @@ static void balloon_up(union dm_msg_info *msg_info) >> long avail_pages; >> unsigned long floor; >> >> - /* The host balloons pages in 2M granularity. */ >> - WARN_ON_ONCE(num_pages % PAGES_IN_2M != 0); >> - >> /* >> * We will attempt 2M allocations. However, if we fail to >> * allocate 2M chunks, we will go back to PAGE_SIZE allocations. >> @@ -1749,14 +1746,13 @@ static void balloon_up(union dm_msg_info *msg_info) >> avail_pages = si_mem_available(); >> floor = compute_balloon_floor(); >> >> - /* Refuse to balloon below the floor, keep the 2M granularity. */ >> + /* Refuse to balloon below the floor. */ >> if (avail_pages < num_pages || avail_pages - num_pages < floor) { >> pr_warn("Balloon request will be partially fulfilled. %s\n", >> avail_pages < num_pages ? "Not enough memory." : >> "Balloon floor reached."); >> >> num_pages = avail_pages > floor ? (avail_pages - floor) : 0; >> - num_pages -= num_pages % PAGES_IN_2M; >> } >> >> while (!done) { >> @@ -1770,7 +1766,7 @@ static void balloon_up(union dm_msg_info *msg_info) >> num_ballooned = alloc_balloon_pages(&dm_device, num_pages, >> bl_resp, alloc_unit); >> >> - if (alloc_unit != 1 && num_ballooned == 0) { >> + if (alloc_unit != 1 && num_ballooned != num_pages) { > > Maybe I'm missing something, but I don't think Vitaly's optimization works. If > alloc_unit specifies 2 Mbytes, and num_pages specifies 3 Mbytes, then num_ballooned > will come back as 2 Mbytes, which is correct. But if we revert alloc_unit to 1 page and > "continue" in that case, we will lose the 2 Mbytes of memory (it's not freed), and the > next time through the loop will try to allocate only 1 Mbyte (because num_pages > will be decremented by num_ballooned). I think the original code does the right thing. > True, nice catch! What I meant to say is that we can avoid sending two replies to the host and get away with just one. Unfortunately, "num_ballooned != num_pages" modification is not sufficient as alloc_balloon_pages() will overwrite bl_resp->range_array[] (as it always starts from 0). I think we can still achieve the goal by allocating bl_resp outside of the loop and filling it from range_array[range_count] instead of range_array[i] but it seems to big of a change for now particular gain. Let's just drop the idea. > Michael > >> alloc_unit = 1; >> continue; >> } >> -- >> 2.14.5 > -- Vitaly