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Howlett" , Qi Zheng Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Barry Song , Kairui Song , Zhang Peng X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=ed25519-sha256; t=1784524064; l=5688; i=zippermonkey@icloud.com; s=20260309; h=from:subject:message-id; bh=vRfWGSnXj1NRnsdshI2zRjQUulhC/QjmbpiKDROQvIQ=; b=EvGUlVN4y70BkfYRM2zX0HE1C0Yr+zYubCcxUThrRzZh/56vO9L1FCC5cpqFHfSBKXSks/K6x ab87sJ8slkXC8FC71/vMjQO1RI+QwEvN7iw8I9vdFs7xRGYx+2jvU/A X-Developer-Key: i=zippermonkey@icloud.com; a=ed25519; pk=tPCLpFnBfIyHsp0k7eaUTUREEa36bQNW/69X+NS8wBU= X-Proofpoint-ORIG-GUID: NROdlRa12C_BqvsJFnYbjXxtk8lK5x-b X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzIwMDA1NCBTYWx0ZWRfX9Qxm5rjC/Y+/ Nyqv2bSDk/Ad1hz66wVCz5lEFOdq1ruTvxVh8zXnAitzw8Lioa4ihJjdbfn9toUKidIR8+jXm1T PYfDTm1JbV7+Bt7WNkH9dFnpHYsXTmjiV8Oc/ZQrpnVI6IqdHFN+MBbMi5LZRiEsSp2nzVLbGRF 5M7za2BW9HVDq/ecRgMVspYC/kvC2wRn67QlDRz3cUced4gnl6mqPOja5Xck3rXtAaZINeFpdFP C86P+xbvl3aaVLJ8GQL812k2UPb6Sx5DA79KlMWXKCqYiqYZWpaioaajzr5eOin97XWGzet02KK 9tcZL8xbjj1Mu0wWWRi X-Proofpoint-GUID: NROdlRa12C_BqvsJFnYbjXxtk8lK5x-b X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 1C57D140005 X-Stat-Signature: 1oicn157rheocw9bda6ox4gfcrju69b6 X-HE-Tag: 1784524106-365503 X-HE-Meta: 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 KZYhVNmu mxxXT/yJBj/K0mFcSTeUjJL6wur2BTYULZLQptHfld1ayne01WsgLF8ukziIBaBnc9GRx2v1Mhej2C2KqheAXsk2FtlFWa17rBa13pytN5+tA5UxCHHYK4CCqdnacp/IYFJDmKdcw191uPOUDPVY6QmpD6pw8elPKIQUWy1WwJWj3sFTPffIOhbRhjIDZJJNbHBCj/CP8iXtmSNmpdu7YkFhwwwSSpUw/jw9E2eXNw1zvaMog5MbHrf+4PFJ6y/tCJ+rccr+bHS99hoETa3NAdgtjyXnj2KQcEnX2tR+diXpz9YFx3YJl2FGLbqBP8xaRTkFd2mfRadtz0EM23MFFu24TmAjUtaxH2BBgJczjVTIgLpZZmKj2Jq+ruwGLE5vJdipSodl3t0MCKRcRrX55+7FtvVniRF4rX+HkwV9S6A0rfKEfPOQvX80GrQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Currently we flush TLB for every dirty folio, which is a bottleneck for systems with many cores as this causes heavy IPI usage. So instead, batch the folios, and flush once for every 31 folios (one folio_batch). These folios will be held in a folio_batch with their lock released, then when the folio_batch is full, do the following steps: - For each folio: trylock - recheck still evictable (writeback, mapped, dma_pinned). If no longer evictable, put back via ret_folios. - Flush TLB once for the whole batch. - Pageout each survivor via folio_try_pageout(). The recheck step is required because dropping the folio lock between shrink_folio_list() and pageout_batch() opens a window in which a parallel swapin (do_swap_page) can fully complete and install a new PTE; once mapped, a parallel GUP can pin the folio without taking the folio lock. Folios caught by any of these checks are put back via ret_folios. Suggested-by: Kairui Song Signed-off-by: Zhang Peng --- mm/vmscan.c | 92 +++++++++++++++++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 84 insertions(+), 8 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index bb479ead1ee0..251535613336 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1220,6 +1220,71 @@ static bool folio_try_pageout(struct folio *folio, return false; } +static void pageout_batch(struct folio_batch *fbatch, + struct list_head *ret_folios, + struct folio_batch *free_folios, + struct scan_control *sc, struct reclaim_stat *stat, + struct swap_iocb **plug, struct list_head *folio_list, + unsigned int *nr_reclaimed) +{ + int i, nr = folio_batch_count(fbatch); + int count = 0; + struct folio *folios[FOLIO_BATCH_SIZE]; + + /* + * Collect survivors into a local array: this avoids walking and + * mutating @fbatch in the same loop, so its invariant (only + * folios[0..nr) are valid) is preserved throughout. + */ + for (i = 0; i < nr; i++) { + struct folio *folio = fbatch->folios[i]; + + if (!folio_trylock(folio)) { + list_add(&folio->lru, ret_folios); + continue; + } + + VM_WARN_ON_FOLIO(folio_test_lru(folio), folio); + + /* + * Recheck what shrink_folio_list() verified before dropping + * the folio lock. Between that folio_unlock() and our + * folio_trylock() here, a parallel swapin (do_swap_page) can + * fully complete -- taking the lock, installing a new PTE, + * and releasing the lock -- after which a parallel GUP + * (O_DIRECT, vmsplice, RDMA, ...) can pin the folio through + * that PTE without taking the folio lock. Each flag catches + * one case: + * folio_test_writeback -- defensive guard. + * folio_mapped -- swapin installed a PTE. + * folio_maybe_dma_pinned -- GUP pinned through such a PTE. + */ + if (folio_test_writeback(folio) || folio_mapped(folio) || + folio_maybe_dma_pinned(folio)) { + folio_unlock(folio); + list_add(&folio->lru, ret_folios); + continue; + } + + folios[count++] = folio; /* keep lock held */ + } + folio_batch_reinit(fbatch); + + if (!count) + return; + + /* One TLB flush for the whole batch */ + try_to_unmap_flush_dirty(); + + for (i = 0; i < count; i++) { + struct folio *folio = folios[i]; + + if (!folio_try_pageout(folio, free_folios, sc, stat, plug, + folio_list, nr_reclaimed)) + list_add(&folio->lru, ret_folios); + } +} + static bool folio_try_unmap(struct folio *folio, struct reclaim_stat *stat, unsigned int nr_pages) { @@ -1261,6 +1326,7 @@ static unsigned int shrink_folio_list(struct list_head *folio_list, struct mem_cgroup *memcg) { struct folio_batch free_folios; + struct folio_batch flush_folios; LIST_HEAD(ret_folios); LIST_HEAD(demote_folios); unsigned int nr_reclaimed = 0, nr_demoted = 0; @@ -1269,6 +1335,7 @@ static unsigned int shrink_folio_list(struct list_head *folio_list, struct swap_iocb *plug = NULL; folio_batch_init(&free_folios); + folio_batch_init(&flush_folios); memset(stat, 0, sizeof(*stat)); cond_resched(); do_demote_pass = can_demote(pgdat->node_id, sc, memcg); @@ -1564,15 +1631,18 @@ static unsigned int shrink_folio_list(struct list_head *folio_list, if (!sc->may_writepage) goto keep_locked; /* - * Folio is dirty. Flush the TLB if a writable entry - * potentially exists to avoid CPU writes after I/O - * starts and then write it out here. + * Drop the lock so swap faults finding this folio + * via swap cache lookup can make progress; the + * recheck that this necessitates is documented in + * pageout_batch(). */ - try_to_unmap_flush_dirty(); - if (!folio_try_pageout(folio, &free_folios, sc, stat, - &plug, folio_list, &nr_reclaimed)) - goto keep; - continue; + folio_unlock(folio); + if (!folio_batch_add(&flush_folios, folio)) + pageout_batch(&flush_folios, + &ret_folios, &free_folios, + sc, stat, &plug, + folio_list, &nr_reclaimed); + goto next; } if (!folio_try_reclaim_free(folio, &free_folios, sc, stat, @@ -1597,6 +1667,12 @@ static unsigned int shrink_folio_list(struct list_head *folio_list, list_add(&folio->lru, &ret_folios); VM_BUG_ON_FOLIO(folio_test_lru(folio) || folio_test_unevictable(folio), folio); +next: + continue; + } + if (folio_batch_count(&flush_folios)) { + pageout_batch(&flush_folios, &ret_folios, &free_folios, sc, + stat, &plug, folio_list, &nr_reclaimed); } /* 'folio_list' is always empty here */ -- 2.43.7