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V14EKoTibMPvaS/zHAcohZjgNl4EWZzXh40yae6m3CQWDqpe+O6wTpxbG4IG5UaY+X2hymCJVl1 Y2FHpolcY6O2dFZcimRclzCQ+N71jyOxlSRp2PAq8GdQKv36s4T4QMQMRfgnuyjHxaoeJCbnQ54 QqAlTBDTAMT6O803sRVSMUVc56Arqi2FXnrR+uXzygYEoSbk6GrDHXCY6aSSuP/HSJxz/c3m63F pEINw/5QjvJlf2x3Q7ohCwMjAfeXAnM7KIKDiccKsJDlQbwCmU8hvoBSY/in8x3WTThDuibB3Xd sibQ3+SGsclrNIfnLjfWVhaqdrE1oxkKYveolTYff21yLFobUQhS6Aacg7Ri0At5hDoI7XytmPS w4YUxW8EUwOT8WYZI4g== X-Authority-Analysis: v=2.4 cv=S4vUAYsP c=1 sm=1 tr=0 ts=69af8f50 cx=c_pps a=XiAAW1AwiKB2Y8Wsi+sD2Q==:117 a=XiAAW1AwiKB2Y8Wsi+sD2Q==:17 a=6eWqkTHjU83fiwn7nKZWdM+Sl24=:19 a=z/mQ4Ysz8XfWz/Q5cLBRGdckG28=:19 a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=xqWC_Br6kY4A:10 a=kj9zAlcOel0A:10 a=Yq5XynenixoA:10 a=GoEa3M9JfhUA:10 a=VkNPw1HP01LnGYTKEx00:22 a=jiCTI4zE5U7BLdzWsZGv:22 a=x0eKOSpe3m1H3M0S9YoZ:22 a=VwQbUJbxAAAA:8 a=pGLkceISAAAA:8 a=yPCof4ZbAAAA:8 a=l4GsR6Set8qm28su0esA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-GUID: V6JY22Y2tIIFOZBPeIvwswWtZ-AgWmnM On Mon, Mar 09, 2026 at 03:00:17PM +0100, vbabka@kernel.org wrote: > On 3/9/26 08:22, Harry Yoo wrote: > > obj_exts_alloc_size() prevents recursive allocation of slabobj_ext > > array from the same cache, to avoid creating slabs that are never freed. > > > > There is one mistake that returns the original size when memory > > allocation profiling is disabled. The assumption was that > > memcg-triggered slabobj_ext allocation is always served from > > KMALLOC_CGROUP type. But this is wrong [1]: when the caller specifies > > both __GFP_RECLAIMABLE and __GFP_ACCOUNT with SLUB_TINY enabled, the > > allocation is served from normal kmalloc. This is because kmalloc_type() > > prioritizes __GFP_RECLAIMABLE over __GFP_ACCOUNT, and SLUB_TINY aliases > > KMALLOC_RECLAIM with KMALLOC_NORMAL. > > Hm that's suboptimal (leads to sparsely used obj_exts in normal kmalloc > slabs) and maybe separately from this hotfix we could make sure that with > SLUB_TINY, __GFP_ACCOUNT is preferred going forward? To be honest, I don't a have strong opinion on that. Is grouping by mobility (for anti-fragmentation less) important on SLUB_TINY systems? > > As a result, the recursion guard is bypassed and the problematic slabs > > can be created. Fix this by removing the mem_alloc_profiling_enabled() > > check entirely. The remaining is_kmalloc_normal() check is still > > sufficient to detect whether the cache is of KMALLOC_NORMAL type and > > avoid bumping the size if it's not. > > > > Without SLUB_TINY, no functional change intended. > > With SLUB_TINY, allocations with __GFP_ACCOUNT|__GFP_RECLAIMABLE > > now allocate a larger array if the sizes equal. > > > > Reported-by: Zw Tang > > Fixes: 280ea9c3154b ("mm/slab: avoid allocating slabobj_ext array from its own slab") > > Closes: https://lore.kernel.org/linux-mm/CAPHJ_VKuMKSke8b11AZQw1PTSFN4n2C0gFxC6xGOG0ZLHgPmnA@mail.gmail.com > > Cc: stable@vger.kernel.org > > Signed-off-by: Harry Yoo > > Added to slab/for-next-fixes, thanks! Thanks! -- Cheers, Harry / Hyeonggon