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See http://www.infradead.org/rpr.html X-Rspamd-Queue-Id: 9E7C710000A X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: t5x7y9bjdpbskixxte9i6b9rqjjzdt8k X-HE-Tag: 1727774374-930362 X-HE-Meta: U2FsdGVkX19tNdUketHNxSO3LpRtjNfT481Bi2tg6/sTtVYRDw0VUubYvqCuaZ2ubikxfReGRfJy7Ndh6/GFRgdqjuqkej8H9tiHjuUSU0NQWl5u/zwVipUZfc1om8BjqvUvi8yH5UNhkHc5IzIETRoOVH13cHnLNv+gkHJrpZkSwtwuHwDO6if7kXUM+WPHYXt/qScHYjzwsPs9JAHUN5oULwjSKlEx4Ny2NHSLMboLuTKMdgK04m+FUXsLTsMy4cK8Yx7pZyj1hr0EC9jU40p5ZgxhUeQKTYVBtEl1EhfJATwvAuf2hd4D1bQOZBrZybpjqo7kiC2Hh5ztfIK1ID1DtUARdYFPieFSPm2IenZY0gyYm7gj6V/qwTU2n0z42gozi00ZFMqP/dLE8y7uDKjojgKZQurWVN0HFprGTysCsH7V4hoS7Ou5R85DunS2kn6fWjEnpd25Pil+lm7hnxh4GbImXome2EjDxZHm8q8hrY+p2hJM2R10XVPrfTFZ1c0l8Cg3Rxvdj6Dw/MVarGi8DQWD14qUIxZn0j78VTTzmuEQsD4xabGhS4EaFEWUe6sBq5suazk4vVrx1HMATK9CcaqTW2XvpXQ/vs3hsvE3ecCR39SEZ4VD877fQksiCOmCQSbHYwDO1KWXTdc7BbNq+0jOKRrxjkiNvitq/YdwkWtAicTz/C0nw3fZ/cnuPnwVqc4dKjxdTZv8iX8Ah7rdYu08ipd85W3DIcWb17oIpG1WtgeA3nuRfMRAixB8S8lOE7mwG+W9/3UOuRYjRCD0m/VyJ06SWh5iWUFhziAb3o9lQRxCIfd41iU3r6nqpg7jxTm+ce7NgwtS13QY+IjQEiJ1ymKf8nPtoTFClUzadxRtyOU2rp62jkLfgy3WLd2Gw0qVTvunD92miTIqEB0moDQcLEwGtV9q2NOxlhkVDSy5EWusaRdcobCrbVhkqOLMlclLajZjRWx9LVE k2cnkmeJ 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 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 Sat, Sep 28, 2024 at 02:15:56PM +0930, Qu Wenruo wrote: > [BACKGROUND] > The function filemap_add_folio() charges the memory cgroup, > as we assume all page caches are accessible by user space progresses > thus needs the cgroup accounting. > > However btrfs is a special case, it has a very large metadata thanks to > its support of data csum (by default it's 4 bytes per 4K data, and can > be as large as 32 bytes per 4K data). > This means btrfs has to go page cache for its metadata pages, to take > advantage of both cache and reclaim ability of filemap. FYI, in general reclaims for metadata work much better with a shrinker than through the pagecache, because it can be object based and prioritized. > [ENHANCEMENT] > Instead of relying on __GFP_NOFAIL to avoid charge failure, use root > memory cgroup to attach metadata pages. > > Although this needs to export the symbol mem_root_cgroup for > CONFIG_MEMCG, or define mem_root_cgroup as NULL for !CONFIG_MEMCG. > > With root memory cgroup, we directly skip the charging part, and only > rely on __GFP_NOFAIL for the real memory allocation part. This looks pretty ugly. What speaks against a version of filemap_add_folio that doesn't charge the memcg?