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[149.14.88.26]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4589539e491sm24168925e9.26.2025.07.30.04.39.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 30 Jul 2025 04:39:40 -0700 (PDT) Message-ID: Date: Wed, 30 Jul 2025 13:39:38 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 4/5] selftests: prctl: introduce tests for disabling THPs completely To: Usama Arif , Andrew Morton , linux-mm@kvack.org, ryan.roberts@arm.com Cc: linux-fsdevel@vger.kernel.org, corbet@lwn.net, rppt@kernel.org, surenb@google.com, mhocko@suse.com, hannes@cmpxchg.org, baohua@kernel.org, shakeel.butt@linux.dev, riel@surriel.com, ziy@nvidia.com, laoar.shao@gmail.com, dev.jain@arm.com, baolin.wang@linux.alibaba.com, npache@redhat.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, jannh@google.com, Arnd Bergmann , sj@kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kernel-team@meta.com References: <20250725162258.1043176-1-usamaarif642@gmail.com> <20250725162258.1043176-5-usamaarif642@gmail.com> <4dc95e54-e0ef-4919-973a-748845897ef9@gmail.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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>>> +    if (!self->pmdsize) >>> +        SKIP(return, "Unable to read PMD size\n"); >>> + >>> +    thp_read_settings(&self->settings); >>> +    self->settings.thp_enabled = THP_MADVISE; >>> +    self->settings.hugepages[sz2ord(self->pmdsize, getpagesize())].enabled = THP_INHERIT; >>> +    thp_save_settings(); >>> +    thp_push_settings(&self->settings); >> >> push without pop, should that be alarming? :) >> >> Can we just use thp_write_settings()? (not sure why that push/pop is required ... is it?) >> > > Thanks for the reviews! > Ack on the previous comments, I have fixed them and will include in next revision. > Yes, I think we can replace thp_push_settings with thp_write_settings. > > For this, I actually just copied what cow.c and uffd-wp-mremap.c are doing :) Right, I see push vs. pop in run_anon_test_case(), but push vs. restore from main(). At least cow.c applies a configuration on top of another one, so it needs the push+pop semantics. In your case, we really only perform a single configuration. So write+restore should be good enough I guess. > > You can see in these 2 files that we do [1] > - thp_read_settings / thp_save_settings > - thp_push_settings > > Than we run the experiment > > and at the end we do [2] > - thp_restore_settings > > i.e. there is no pop. > > I think we can change the thp_push_settings to thp_write_settings in [3] and [4] as well? I think we have to push there, so the following push+pop will do the right thing (I think that was the whole idea of push+pop). An alternative would have been to just have write+restore, whereby write always returns the old state you save in a local variable. I wonder if a final pop could be used instead of the restore somehow. Anyhow, probably best to leave the other test cases alone for now, unless you want to clean it up properly :) [...] >>> +} >>> + >>> +FIXTURE_TEARDOWN(prctl_thp_disable_completely) >>> +{> +    thp_restore_settings(); >>> +} >>> + >>> +/* prctl_thp_disable_except_madvise fixture sets system THP setting to madvise */ >>> +static void prctl_thp_disable_completely(struct __test_metadata *const _metadata, >>> +                     size_t pmdsize) >>> +{ >>> +    int res = 0; >>> + >>> +    res = prctl(PR_GET_THP_DISABLE, NULL, NULL, NULL, NULL); >>> +    ASSERT_EQ(res, 1); >>> + >>> +    /* global = madvise, process = never, we shouldn't get HPs even with madvise */ >> >> s/HPs/THPs/ >> >>> +    res = test_mmap_thp(NONE, pmdsize); >>> +    ASSERT_EQ(res, 0); >>> + >>> +    res = test_mmap_thp(HUGE, pmdsize); >>> +    ASSERT_EQ(res, 0); >>> + >>> +    res = test_mmap_thp(COLLAPSE, pmdsize); >>> +    ASSERT_EQ(res, 0); >>> + >>> +    /* Reset to system policy */ >>> +    res =  prctl(PR_SET_THP_DISABLE, 0, NULL, NULL, NULL); >>> +    ASSERT_EQ(res, 0); >>> + >>> +    /* global = madvise */ >>> +    res = test_mmap_thp(NONE, pmdsize); >>> +    ASSERT_EQ(res, 0); >>> + >>> +    res = test_mmap_thp(HUGE, pmdsize); >>> +    ASSERT_EQ(res, 1); >>> + >>> +    res = test_mmap_thp(COLLAPSE, pmdsize); >>> +    ASSERT_EQ(res, 1); >> >> >> Makes me wonder: should we test for global=always and global=always? > > Do you mean global=madvise and global=always?> Yeah, rewrote it 3 times and then messed it up. >> (or simply for all possible values, including global=never if easily possible?) >> >> At least testing with global=always should exercise more possible paths >> than global=always (esp., test_mmap_thp(NONE, pmdsize) which would >> never apply in madvise mode). >> > > lol I think over here as well you meant madvise in the 2nd instance. Yeah :) > > I was just looking at other selftests and I saw FIXTURE_VARIANT_ADD, I think we can > use that to do it without replicating too much code. Let me see if I > can use that and do it for never, madvise and always. If it doesnt help > there might be some code replication, but that should be ok. Yeah, some easy way without replicating would be very nice. -- Cheers, David / dhildenb