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[99.241.198.116]) by smtp.gmail.com with ESMTPSA id j9-20020a056e020ee900b002cbfe66d86csm10161839ilk.68.2022.04.27.13.47.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 27 Apr 2022 13:47:44 -0700 (PDT) Date: Wed, 27 Apr 2022 16:47:41 -0400 From: Peter Xu To: Zach O'Keefe Cc: Alex Shi , David Hildenbrand , David Rientjes , Matthew Wilcox , Michal Hocko , Pasha Tatashin , SeongJae Park , Song Liu , Vlastimil Babka , Yang Shi , Zi Yan , linux-mm@kvack.org, Andrea Arcangeli , Andrew Morton , Arnd Bergmann , Axel Rasmussen , Chris Kennelly , Chris Zankel , Helge Deller , Hugh Dickins , Ivan Kokshaysky , "James E.J. Bottomley" , Jens Axboe , "Kirill A. Shutemov" , Matt Turner , Max Filippov , Miaohe Lin , Minchan Kim , Patrick Xia , Pavel Begunkov , Thomas Bogendoerfer Subject: Re: [PATCH v3 04/12] mm/khugepaged: add struct collapse_result Message-ID: References: <20220426144412.742113-1-zokeefe@google.com> <20220426144412.742113-5-zokeefe@google.com> MIME-Version: 1.0 In-Reply-To: <20220426144412.742113-5-zokeefe@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/mixed; boundary="mgC1V9TUYNZCLjK2" Content-Disposition: inline X-Stat-Signature: mkucys7yoqc68wpy933hysacq5hie6o9 X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 19AA614004C Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=S389iCMC; spf=none (imf09.hostedemail.com: domain of peterx@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspam-User: X-HE-Tag: 1651092463-9670 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: --mgC1V9TUYNZCLjK2 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline On Tue, Apr 26, 2022 at 07:44:04AM -0700, Zach O'Keefe wrote: > +/* Gather information from one khugepaged_scan_[pmd|file]() request */ > +struct collapse_result { > + enum scan_result result; > + > + /* Was mmap_lock dropped during request? */ > + bool dropped_mmap_lock; > +}; IMHO this new dropped_mmap_lock makes things a bit more complicated.. To me, the old code actually is easy to read on when the lock is dropped: - For file, we always drop it - For anon, when khugepaged_scan_pmd() returns 1 That's fairly clear to me. But I understand what you need, probably the "result" hidden in the old world but you'd need that for MADV_COLLAPSE? I also noticed major chunks of this patch is converting "result = XXX" into "cr->result = XXX". IMHO that's really not necessary for touching up all the places around. I'm also wondering whether we could simply pass over the result into your newly introduced collapse_control*. In summary, this is what's in my mind.. - Add collapse_control.result - Make sure both khugepaged_scan_file() and khugepaged_scan_pmd() to simply remember to update cc->result before it returns I've attached a pesudo code patch (note! it's pesudo not even compile but to show what I meant..), so far I don't see a problem with it. -- Peter Xu --mgC1V9TUYNZCLjK2 Content-Type: text/plain; charset=utf-8 Content-Disposition: attachment; filename=patch diff --git a/mm/khugepaged.c b/mm/khugepaged.c index d7c5bb9fd1fb..bd341115d359 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1040,7 +1040,7 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm, return true; } -static void collapse_huge_page(struct mm_struct *mm, +static int collapse_huge_page(struct mm_struct *mm, unsigned long address, struct page **hpage, int node, int referenced, int unmapped) @@ -1208,7 +1208,7 @@ static void collapse_huge_page(struct mm_struct *mm, if (!IS_ERR_OR_NULL(*hpage)) mem_cgroup_uncharge(page_folio(*hpage)); trace_mm_collapse_huge_page(mm, isolated, result); - return; + return result; } static int khugepaged_scan_pmd(struct mm_struct *mm, @@ -1361,13 +1361,19 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, pte_unmap_unlock(pte, ptl); if (ret) { node = khugepaged_find_target_node(); - /* collapse_huge_page will return with the mmap_lock released */ - collapse_huge_page(mm, address, hpage, node, - referenced, unmapped); + /* + * collapse_huge_page will return with the mmap_lock + * released. It'll also further update cc->result if + * anything wrong happens. + */ + result = collapse_huge_page(mm, address, hpage, node, + referenced, unmapped, cc); } out: trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced, none_or_zero, result, unmapped); + /* Deliver the result to the caller */ + cc->result = result; return ret; } @@ -1646,7 +1652,7 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff) * + restore gaps in the page cache; * + unlock and free huge page; */ -static void collapse_file(struct mm_struct *mm, +static int collapse_file(struct mm_struct *mm, struct file *file, pgoff_t start, struct page **hpage, int node) { @@ -2009,6 +2015,7 @@ static void collapse_file(struct mm_struct *mm, if (!IS_ERR_OR_NULL(*hpage)) mem_cgroup_uncharge(page_folio(*hpage)); /* TODO: tracepoints */ + return result; } static void khugepaged_scan_file(struct mm_struct *mm, @@ -2086,11 +2093,12 @@ static void khugepaged_scan_file(struct mm_struct *mm, count_vm_event(THP_SCAN_EXCEED_NONE_PTE); } else { node = khugepaged_find_target_node(); - collapse_file(mm, file, start, hpage, node); + result = collapse_file(mm, file, start, hpage, node); } } /* TODO: tracepoints */ + cc->result = result; } #else static void khugepaged_scan_file(struct mm_struct *mm, --mgC1V9TUYNZCLjK2--