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 826S958m cKUxIDFYu+weXjt1rq7Cj1c9OTQPU+RLEx0oLzghLw5PsTX0= 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: List-Subscribe: List-Unsubscribe: On 6 Feb 2026, at 13:33, Zi Yan wrote: > Hit send too soon, sorry about that. > > On 6 Feb 2026, at 13:29, Zi Yan wrote: > >> On 6 Feb 2026, at 13:21, Mikhail Gavrilov wrote: >> >>> Hi, Yan >>> >>> On Fri, Feb 6, 2026 at 11:08=E2=80=AFPM Zi Yan wrote: >>>> >>>> Do you have a reproducer for this issue? >>> >>> Yes, I have a stress test that reliably reproduces the crash. >>> It cycles swapon/swapoff on 8GB zram under memory pressure: >>> https://gist.github.com/NTMan/4ed363793ebd36bd702a39283f06cee1 > > Got it. > > Merging replies from Kairui from another email: > > This patch is from previous discussion: > https://lore.kernel.org/linux-mm/CABXGCsO3XcXt5GDae7d74ynC6P6G2gLw3ZrwAYv= SQ3PwP0mGXA@mail.gmail.com/ > > It looks odd to me too. That bug starts with vmalloc dropping > __GFP_COMP in commit 3b8000ae185c, because with __GFP_COMP, the > allocator does clean the ->private of tail pages on allocation with > prep_compound_page. Without __GFP_COMP, these ->private fields are > left as it is. > >>> >>>> Last time I checked page->private usage, I find users clears ->private= before free a page. >>>> I wonder which one I was missing. >>> >>> The issue is not about freeing - it's about allocation. > > I assume everyone zeros used ->private, head or tail, so PageBuddy has > all zeroed ->private. > >>> When buddy allocator merges/splits pages, it uses page->private to stor= e order. >>> When a high-order page is later allocated and split via split_page(), >>> tail pages still have their old page->private values. > > No, in __free_one_page(), if a free page is merged to a higher order, > it is deleted from free list and its ->private is zeroed. There should no= t > be any non zero private. > >>> The path is: >>> 1. Page freed =E2=86=92 free_pages_prepare() does NOT clear page->priva= te > > Right. The code assume page->private is zero for all pages, head or tail > if it is compound. > >>> 2. Page goes to buddy allocator =E2=86=92 buddy uses page->private for = order >>> 3. Page allocated as high-order =E2=86=92 post_alloc_hook() only clears= head >>> page's private >>> 4. split_page() called =E2=86=92 tail pages keep stale page->private >>> >>>> Clearing ->private in split_page() looks like a hack instead of a fix. >>> >>> I discussed this with Kairui Song earlier in the thread. We considered: >>> >>> 1. Fix in post_alloc_hook() - would need to clear all pages, not just h= ead >>> 2. Fix in swapfile.c - doesn't work because stale value could >>> accidentally equal SWP_CONTINUED >>> 3. Fix in split_page() - ensures pages are properly initialized for >>> independent use >>> >>> The comment in vmalloc.c says split pages should be usable >>> independently ("some use page->mapping, page->lru, etc."), so >>> split_page() initializing the pages seems appropriate. >>> >>> But I agree post_alloc_hook() might be a cleaner place. Would you >>> prefer a patch there instead? > > I think it is better to find out which code causes non zero ->private > at page free time. Hi Mikhail, Do you mind sharing the kernel config? I am trying to reproduce it locally but have no luck (Iteration 111 and going) so far. Thanks. Best Regards, Yan, Zi