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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Shuah Khan , Kevin Brodsky , linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] kselftest: mm: prevent random failure of huge page split for khugepaged Message-ID: References: <20260820-fix_split-v1-0-ab430c58c7cf@arm.com> <20260820-fix_split-v1-1-ab430c58c7cf@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Stat-Signature: pocjiuury81tgdsqxwdxpctgdeadtibh X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 9040F40004 X-HE-Tag: 1787270113-812918 X-HE-Meta: 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 4xkM82bf Yn2pRqDSg1GnfSqH4Nso1znuP7mvPuC6wTKF3GxNgKtAL9UOj6wXx5u6xafPm/h/LpapS+AixZYx8iMb9eLXHAeNUkaEE2m5v4Yuj09JmudeQzAjQqU/OmvJQbdKjp6UDGuAsHM5HLxAv9jCRVC2x6ULBdFhGGJbt1zv7FWZejoOTZgDpzMrU5tXttqM2OVrz0P75TOW/xNNo2R0zBfYHk7CsFOkrIDodhdgfibpVtWVEkJuncLGVCBpoe+s7xtFgSy00 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Aug 20, 2026 at 07:37:29PM -0400, Zi Yan wrote: > On Thu Aug 20, 2026 at 5:23 PM EDT, Yeoreum Yun wrote: > > On Thu, Aug 20, 2026 at 03:51:34PM -0400, Zi Yan wrote: > >> On Thu Aug 20, 2026 at 3:40 PM EDT, Yeoreum Yun wrote: > >> > There're some random failure for split_huge_page_test when khugepaged > >> > collapses pages into pmd again which had split by the test. > >> > > >> > Prevent the khugepaged's collapses for split page by setting the > >> > mapped pmd-huge-page with MADV_NOHUGEPAGE before split. > >> > >> Why not disable khugepaged using APIs from hugepage_setting.h? > > > > Well, this also works with hugepage_save_settings() and write the > > khugepaged/scan_sleep_millisecs with the maximum integer. > > > > I don't have a strong opinion but since it seems more hackish way to > > change scan_sllep_millisecs, I use madvise() with MADV_NOHUGEPATE. > > > > Would it be better to change using APIs in hugepage_setting,h? > > No. I did not realize there is no way of stopping khugepaged completely. > > BTW, I am curious about your khugepaged config causing this issue. > IIRC, khugepaged scan interval is about minutes and > the time between madvise(MADV_HUGEPAGE) and the second > is_backed_by_folio() should not be that long. Yes. it's relly timing sensitive and I've failed to reproduce in the real hardware. but in the emulation environment it often failed with the scan_sllep_millisecs as 10 seconds while the test running. > > For your patch, maybe you want to check the return value of madvise() to > make sure it succeeds. Yeap. but it seems enough just worning message for the madvise() with MADV_NOHUGEPAGE. > > Otherwise, > > feel free to add > > Reviewed-by: Zi Yan Thanks! -- Sincerely, Yeoreum Yun