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Tue, 6 Feb 2024 10:09:22 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id G274NVIFwmV8egAAD6G6ig (envelope-from ); Tue, 06 Feb 2024 10:09:22 +0000 Date: Tue, 6 Feb 2024 11:09:18 +0100 From: Michal Hocko To: Baolin Wang Cc: akpm@linux-foundation.org, muchun.song@linux.dev, osalvador@suse.de, david@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] mm: hugetlb: improve the handling of hugetlb allocation failure for freed or in-use hugetlb Message-ID: References: <62890fd60b1ecd5bf1cdc476c973f60fe37aa0cb.1707181934.git.baolin.wang@linux.alibaba.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <62890fd60b1ecd5bf1cdc476c973f60fe37aa0cb.1707181934.git.baolin.wang@linux.alibaba.com> X-Spam-Level: Authentication-Results: smtp-out1.suse.de; dkim=pass header.d=suse.com header.s=susede1 header.b=RWRxrMyN X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Spamd-Result: default: False [-6.01 / 50.00]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; R_DKIM_ALLOW(-0.20)[suse.com:s=susede1]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; MIME_GOOD(-0.10)[text/plain]; DWL_DNSWL_MED(-2.00)[suse.com:dkim]; NEURAL_HAM_SHORT(-0.20)[-1.000]; RCVD_COUNT_THREE(0.00)[3]; DKIM_SIGNED(0.00)[suse.com:s=susede1]; DKIM_TRACE(0.00)[suse.com:+]; MX_GOOD(-0.01)[]; RCPT_COUNT_SEVEN(0.00)[7]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.com:dkim,suse.com:email]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; MID_RHS_NOT_FQDN(0.50)[]; RCVD_TLS_ALL(0.00)[]; BAYES_HAM(-3.00)[100.00%] X-Spam-Score: -6.01 X-Rspamd-Queue-Id: E460B220ED X-Spam-Flag: NO On Tue 06-02-24 11:08:11, Baolin Wang wrote: > alloc_and_dissolve_hugetlb_folio() preallocates a new hugetlb page before > it takes hugetlb_lock. In 3 out of 4 cases the page is not really used and > therefore the newly allocated page is just freed right away. This is > wasteful and it might cause pre-mature failures in those cases. > > Address that by moving the allocation down to the only case (hugetlb > page is really in the free pages pool). We need to drop hugetlb_lock > to do so and therefore need to recheck the page state after regaining > it. > > The patch is more of a cleanup than an actual fix to an existing > problem. There are no known reports about pre-mature failures. > > Signed-off-by: Baolin Wang Acked-by: Michal Hocko Thanks! > --- > Changes from v2； > - Update the commit message suggested by Michal. > - Remove unnecessary comments. > Changes from v1: > - Update the suject line per Muchun. > - Move the allocation into the free hugetlb handling branch per Michal. > --- > mm/hugetlb.c | 32 ++++++++++++++++---------------- > 1 file changed, 16 insertions(+), 16 deletions(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 9d996fe4ecd9..a05507a2143f 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -3031,21 +3031,9 @@ static int alloc_and_dissolve_hugetlb_folio(struct hstate *h, > { > gfp_t gfp_mask = htlb_alloc_mask(h) | __GFP_THISNODE; > int nid = folio_nid(old_folio); > - struct folio *new_folio; > + struct folio *new_folio = NULL; > int ret = 0; > > - /* > - * Before dissolving the folio, we need to allocate a new one for the > - * pool to remain stable. Here, we allocate the folio and 'prep' it > - * by doing everything but actually updating counters and adding to > - * the pool. This simplifies and let us do most of the processing > - * under the lock. > - */ > - new_folio = alloc_buddy_hugetlb_folio(h, gfp_mask, nid, NULL, NULL); > - if (!new_folio) > - return -ENOMEM; > - __prep_new_hugetlb_folio(h, new_folio); > - > retry: > spin_lock_irq(&hugetlb_lock); > if (!folio_test_hugetlb(old_folio)) { > @@ -3075,6 +3063,16 @@ static int alloc_and_dissolve_hugetlb_folio(struct hstate *h, > cond_resched(); > goto retry; > } else { > + if (!new_folio) { > + spin_unlock_irq(&hugetlb_lock); > + new_folio = alloc_buddy_hugetlb_folio(h, gfp_mask, nid, > + NULL, NULL); > + if (!new_folio) > + return -ENOMEM; > + __prep_new_hugetlb_folio(h, new_folio); > + goto retry; > + } > + > /* > * Ok, old_folio is still a genuine free hugepage. Remove it from > * the freelist and decrease the counters. These will be > @@ -3102,9 +3100,11 @@ static int alloc_and_dissolve_hugetlb_folio(struct hstate *h, > > free_new: > spin_unlock_irq(&hugetlb_lock); > - /* Folio has a zero ref count, but needs a ref to be freed */ > - folio_ref_unfreeze(new_folio, 1); > - update_and_free_hugetlb_folio(h, new_folio, false); > + if (new_folio) { > + /* Folio has a zero ref count, but needs a ref to be freed */ > + folio_ref_unfreeze(new_folio, 1); > + update_and_free_hugetlb_folio(h, new_folio, false); > + } > > return ret; > } > -- > 2.39.3 > -- Michal Hocko SUSE Labs