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b=IFlwAlOACBc1t0eTA75hgfLQoomakaAr0V++zYog30tub5f0bGHHlgXjZfX7+lx+m 8L7n5fUfkLsF3nQU/Smmq0LqztVRyoxyiFMKDY0eERzbsa5CJprVeK9S+B5Gq9BaPz j2ld+5pBA+XBGCSMXVOJgeRgbM4XcqSrKC+Iqc6okQRlL6VGPOyofdCrF0b1yJ3TiK QEwy1gdo27047Db308U+70mAo3nnS3DIOWsfliNrDNw5Ui0Ucea2ksVRlMfm20mmEj ygjUhnEYFctt/oHQVvtVDZOMAnRjgZ+auCvDtpHomOLQ1T718lwE9yjUa4kFJD300s ZCXBClMgfZyMA== From: Pratyush Yadav To: Chenghao Duan Cc: pasha.tatashin@soleen.com, rppt@kernel.org, pratyush@kernel.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, jianghaoran@kylinos.cn Subject: Re: [PATCH v1 1/3] mm/memfd_luo: optimize shmem_recalc_inode calls in retrieve path In-Reply-To: <20260319012845.29570-2-duanchenghao@kylinos.cn> (Chenghao Duan's message of "Thu, 19 Mar 2026 09:28:43 +0800") References: <20260319012845.29570-1-duanchenghao@kylinos.cn> <20260319012845.29570-2-duanchenghao@kylinos.cn> Date: Fri, 20 Mar 2026 10:02:49 +0000 Message-ID: <2vxzikaqbyye.fsf@kernel.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Stat-Signature: qbpgai9o5xmms333rdggneqj46hnf9mf X-Rspamd-Server: rspam09 X-Rspam-User: X-Rspamd-Queue-Id: 7B0094000E X-HE-Tag: 1774000974-601775 X-HE-Meta: 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 LUav0euC wmmrQDFWVGkxKyJLFg6nxrBxgu1Li2YPDixUcTrZJtce/cktJjofJNpXHBVUEWDvgwS37L+LaJW2+Z1gBkhKrRS9UELF+V83GL8WSua893hracvUQwwVWoyWTf68v/bYrkZL8WSDp+MOcT4Swf3d2AZcWUNwDB9FEjBbBxaAk5fmxKyzO94LE62w1nvkk/Txx9IVqxQcOix1MMEGL7LS3uVeRwlcVvFDTM2qsmRrFmTuuzillzYHdP6cd7sgz6WylqCdO/NP2cHG1np7bqdsto09zzA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Mar 19 2026, Chenghao Duan wrote: > Move shmem_recalc_inode() out of the loop in memfd_luo_retrieve_folios() > to improve performance when restoring large memfds. > > Currently, shmem_recalc_inode() is called for each folio during restore, > which is O(n) expensive operations. This patch collects the number of > successfully added folios and calls shmem_recalc_inode() once after the > loop completes, reducing complexity to O(1). > > Additionally, fix the error path to also call shmem_recalc_inode() for > the folios that were successfully added before the error occurred. > > Signed-off-by: Chenghao Duan > --- > mm/memfd_luo.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/mm/memfd_luo.c b/mm/memfd_luo.c > index b8edb9f981d7..5ddd3657d8be 100644 > --- a/mm/memfd_luo.c > +++ b/mm/memfd_luo.c > @@ -397,6 +397,7 @@ static int memfd_luo_retrieve_folios(struct file *file, > struct folio *folio; > int err = -EIO; > long i; > + u64 nr_added = 0; > > for (i = 0; i < nr_folios; i++) { > const struct memfd_luo_folio_ser *pfolio = &folios_ser[i]; > @@ -448,12 +449,15 @@ static int memfd_luo_retrieve_folios(struct file *file, > goto unlock_folio; > } > > - shmem_recalc_inode(inode, 1, 0); > + nr_added++; https://sashiko.dev/#/patchset/20260319012845.29570-1-duanchenghao%40kylinos.cn AI review picked up a real bug here: Since memfd files can use large folios, should nr_added track the number of pages instead of the number of folios? shmem_recalc_inode() expects the number of pages. Passing the number of folios might under-account blocks and bypass tmpfs limits or quotas. Also, shmem_inode_acct_blocks() earlier in the loop is hardcoded to 1, which might have the same issue. If THP is being used, we should account for nr_pages instead of nr_folios. Can you please also add a fix for this with your series? Just so we fix the bugs the code already has before refactoring it. > folio_add_lru(folio); > folio_unlock(folio); > folio_put(folio); > } > > + if (nr_added) > + shmem_recalc_inode(inode, nr_added, 0); Nit: it is very very likely that nr_added > 0. And shmem_recalc_inode() can deal with 0 nr_added. So please drop this if check and call it directly. Other than this, the patch LGTM. Thanks for working on this! > + > return 0; > > unlock_folio: > @@ -472,6 +476,9 @@ static int memfd_luo_retrieve_folios(struct file *file, > folio_put(folio); > } > > + if (nr_added) > + shmem_recalc_inode(inode, nr_added, 0); > + > return err; > } -- Regards, Pratyush Yadav