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bh=iFy1afwZ49iaQxrTI06bp2qGek5VGg2+6csG1O4bfHg=; b=aHQDmCrwFzttauoQVC0MAO84WrFiMbVMaspuVP61MOGZZm//VXh7jxcFQktA6ydkXS1hdk QBz5KwvRQaVv72Dg== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 6BBDC593A8; Mon, 18 May 2026 20:53:48 +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 iXRvD1x8C2oWeAAAD6G6ig (envelope-from ); Mon, 18 May 2026 20:53:48 +0000 From: Fabiano Rosas To: Bin Guo , qemu-devel@nongnu.org Cc: peterx@redhat.com Subject: Re: [PATCH 4/8] migration/savevm: use stack-allocated bitmap in configuration_validate_capabilities In-Reply-To: <20260518110112.21395-5-guobin@linux.alibaba.com> References: <20260518110112.21395-1-guobin@linux.alibaba.com> <20260518110112.21395-5-guobin@linux.alibaba.com> Date: Mon, 18 May 2026 17:53:45 -0300 Message-ID: <8733zo4exy.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Action: no action X-Spamd-Result: default: False [-4.51 / 50.00]; BAYES_HAM(-3.00)[99.99%]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCVD_TLS_ALL(0.00)[]; MISSING_XM_UA(0.00)[]; TO_DN_SOME(0.00)[]; MIME_TRACE(0.00)[0:+]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; FUZZY_RATELIMITED(0.00)[rspamd.com]; MID_RHS_MATCH_FROM(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_THREE(0.00)[3]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email,suse.de:dkim,suse.de:mid]; DKIM_TRACE(0.00)[suse.de:+] X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Rspamd-Queue-Id: CB2D464188 Received-SPF: pass client-ip=195.135.223.130; envelope-from=farosas@suse.de; helo=smtp-out1.suse.de X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Bin Guo writes: > configuration_validate_capabilities() allocates a bitmap on the heap > to track source capabilities via bitmap_new()/g_free(). Since > MIGRATION_CAPABILITY__MAX is a small compile-time constant (< 64), > a heap allocation for a bitmap this small is wasteful: it adds > malloc/free overhead and a potential cache miss for a transient > 8-byte allocation. > > Replace with DECLARE_BITMAP() on the stack and bitmap_zero() to > initialize. This eliminates the heap round-trip entirely. > > Signed-off-by: Bin Guo > --- > migration/savevm.c | 5 ++--- > 1 file changed, 2 insertions(+), 3 deletions(-) > > diff --git a/migration/savevm.c b/migration/savevm.c > index d1dd696c17..23adaf9dd9 100644 > --- a/migration/savevm.c > +++ b/migration/savevm.c > @@ -347,10 +347,10 @@ static bool configuration_validate_capabilities(SaveState *state) > { > bool ret = true; > MigrationState *s = migrate_get_current(); > - unsigned long *source_caps_bm; > + DECLARE_BITMAP(source_caps_bm, MIGRATION_CAPABILITY__MAX); > int i; > > - source_caps_bm = bitmap_new(MIGRATION_CAPABILITY__MAX); > + bitmap_zero(source_caps_bm, MIGRATION_CAPABILITY__MAX); > for (i = 0; i < state->caps_count; i++) { > MigrationCapability capability = state->capabilities[i]; > set_bit(capability, source_caps_bm); > @@ -373,7 +373,6 @@ static bool configuration_validate_capabilities(SaveState *state) > } > } > > - g_free(source_caps_bm); > return ret; > } Reviewed-by: Fabiano Rosas